Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 3301 insertions, 0 deletions

diff --git a/third_party/rust/cc/src/lib.rs b/third_party/rust/cc/src/lib.rs
new file mode 100644
index 0000000000..e3a2b98b03
--- /dev/null
+++ b/third_party/rust/cc/src/lib.rs
@@ -0,0 +1,3301 @@
+//! A library for build scripts to compile custom C code
+//!
+//! This library is intended to be used as a `build-dependencies` entry in
+//! `Cargo.toml`:
+//!
+//! ```toml
+//! [build-dependencies]
+//! cc = "1.0"
+//! ```
+//!
+//! The purpose of this crate is to provide the utility functions necessary to
+//! compile C code into a static archive which is then linked into a Rust crate.
+//! Configuration is available through the `Build` struct.
+//!
+//! This crate will automatically detect situations such as cross compilation or
+//! other environment variables set by Cargo and will build code appropriately.
+//!
+//! The crate is not limited to C code, it can accept any source code that can
+//! be passed to a C or C++ compiler. As such, assembly files with extensions
+//! `.s` (gcc/clang) and `.asm` (MSVC) can also be compiled.
+//!
+//! [`Build`]: struct.Build.html
+//!
+//! # Parallelism
+//!
+//! To parallelize computation, enable the `parallel` feature for the crate.
+//!
+//! ```toml
+//! [build-dependencies]
+//! cc = { version = "1.0", features = ["parallel"] }
+//! ```
+//! To specify the max number of concurrent compilation jobs, set the `NUM_JOBS`
+//! environment variable to the desired amount.
+//!
+//! Cargo will also set this environment variable when executed with the `-jN` flag.
+//!
+//! If `NUM_JOBS` is not set, the `RAYON_NUM_THREADS` environment variable can
+//! also specify the build parallelism.
+//!
+//! # Examples
+//!
+//! Use the `Build` struct to compile `src/foo.c`:
+//!
+//! ```no_run
+//! fn main() {
+//!     cc::Build::new()
+//!         .file("src/foo.c")
+//!         .define("FOO", Some("bar"))
+//!         .include("src")
+//!         .compile("foo");
+//! }
+//! ```
+
+#![doc(html_root_url = "https://docs.rs/cc/1.0")]
+#![cfg_attr(test, deny(warnings))]
+#![allow(deprecated)]
+#![deny(missing_docs)]
+
+use std::collections::HashMap;
+use std::env;
+use std::ffi::{OsStr, OsString};
+use std::fmt::{self, Display};
+use std::fs;
+use std::io::{self, BufRead, BufReader, Read, Write};
+use std::path::{Component, Path, PathBuf};
+use std::process::{Child, Command, Stdio};
+use std::sync::{Arc, Mutex};
+use std::thread::{self, JoinHandle};
+
+// These modules are all glue to support reading the MSVC version from
+// the registry and from COM interfaces
+#[cfg(windows)]
+mod registry;
+#[cfg(windows)]
+#[macro_use]
+mod winapi;
+#[cfg(windows)]
+mod com;
+#[cfg(windows)]
+mod setup_config;
+#[cfg(windows)]
+mod vs_instances;
+
+pub mod windows_registry;
+
+/// A builder for compilation of a native library.
+///
+/// A `Build` is the main type of the `cc` crate and is used to control all the
+/// various configuration options and such of a compile. You'll find more
+/// documentation on each method itself.
+#[derive(Clone, Debug)]
+pub struct Build {
+    include_directories: Vec<PathBuf>,
+    definitions: Vec<(String, Option<String>)>,
+    objects: Vec<PathBuf>,
+    flags: Vec<String>,
+    flags_supported: Vec<String>,
+    known_flag_support_status: Arc<Mutex<HashMap<String, bool>>>,
+    ar_flags: Vec<String>,
+    no_default_flags: bool,
+    files: Vec<PathBuf>,
+    cpp: bool,
+    cpp_link_stdlib: Option<Option<String>>,
+    cpp_set_stdlib: Option<String>,
+    cuda: bool,
+    cudart: Option<String>,
+    target: Option<String>,
+    host: Option<String>,
+    out_dir: Option<PathBuf>,
+    opt_level: Option<String>,
+    debug: Option<bool>,
+    force_frame_pointer: Option<bool>,
+    env: Vec<(OsString, OsString)>,
+    compiler: Option<PathBuf>,
+    archiver: Option<PathBuf>,
+    cargo_metadata: bool,
+    pic: Option<bool>,
+    use_plt: Option<bool>,
+    static_crt: Option<bool>,
+    shared_flag: Option<bool>,
+    static_flag: Option<bool>,
+    warnings_into_errors: bool,
+    warnings: Option<bool>,
+    extra_warnings: Option<bool>,
+    env_cache: Arc<Mutex<HashMap<String, Option<String>>>>,
+    apple_sdk_root_cache: Arc<Mutex<HashMap<String, OsString>>>,
+}
+
+/// Represents the types of errors that may occur while using cc-rs.
+#[derive(Clone, Debug)]
+enum ErrorKind {
+    /// Error occurred while performing I/O.
+    IOError,
+    /// Invalid architecture supplied.
+    ArchitectureInvalid,
+    /// Environment variable not found, with the var in question as extra info.
+    EnvVarNotFound,
+    /// Error occurred while using external tools (ie: invocation of compiler).
+    ToolExecError,
+    /// Error occurred due to missing external tools.
+    ToolNotFound,
+    /// One of the function arguments failed validation.
+    InvalidArgument,
+}
+
+/// Represents an internal error that occurred, with an explanation.
+#[derive(Clone, Debug)]
+pub struct Error {
+    /// Describes the kind of error that occurred.
+    kind: ErrorKind,
+    /// More explanation of error that occurred.
+    message: String,
+}
+
+impl Error {
+    fn new(kind: ErrorKind, message: &str) -> Error {
+        Error {
+            kind: kind,
+            message: message.to_owned(),
+        }
+    }
+}
+
+impl From<io::Error> for Error {
+    fn from(e: io::Error) -> Error {
+        Error::new(ErrorKind::IOError, &format!("{}", e))
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{:?}: {}", self.kind, self.message)
+    }
+}
+
+impl std::error::Error for Error {}
+
+/// Configuration used to represent an invocation of a C compiler.
+///
+/// This can be used to figure out what compiler is in use, what the arguments
+/// to it are, and what the environment variables look like for the compiler.
+/// This can be used to further configure other build systems (e.g. forward
+/// along CC and/or CFLAGS) or the `to_command` method can be used to run the
+/// compiler itself.
+#[derive(Clone, Debug)]
+pub struct Tool {
+    path: PathBuf,
+    cc_wrapper_path: Option<PathBuf>,
+    cc_wrapper_args: Vec<OsString>,
+    args: Vec<OsString>,
+    env: Vec<(OsString, OsString)>,
+    family: ToolFamily,
+    cuda: bool,
+    removed_args: Vec<OsString>,
+}
+
+/// Represents the family of tools this tool belongs to.
+///
+/// Each family of tools differs in how and what arguments they accept.
+///
+/// Detection of a family is done on best-effort basis and may not accurately reflect the tool.
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum ToolFamily {
+    /// Tool is GNU Compiler Collection-like.
+    Gnu,
+    /// Tool is Clang-like. It differs from the GCC in a sense that it accepts superset of flags
+    /// and its cross-compilation approach is different.
+    Clang,
+    /// Tool is the MSVC cl.exe.
+    Msvc { clang_cl: bool },
+}
+
+impl ToolFamily {
+    /// What the flag to request debug info for this family of tools look like
+    fn add_debug_flags(&self, cmd: &mut Tool) {
+        match *self {
+            ToolFamily::Msvc { .. } => {
+                cmd.push_cc_arg("-Z7".into());
+            }
+            ToolFamily::Gnu | ToolFamily::Clang => {
+                cmd.push_cc_arg("-g".into());
+            }
+        }
+    }
+
+    /// What the flag to force frame pointers.
+    fn add_force_frame_pointer(&self, cmd: &mut Tool) {
+        match *self {
+            ToolFamily::Gnu | ToolFamily::Clang => {
+                cmd.push_cc_arg("-fno-omit-frame-pointer".into());
+            }
+            _ => (),
+        }
+    }
+
+    /// What the flags to enable all warnings
+    fn warnings_flags(&self) -> &'static str {
+        match *self {
+            ToolFamily::Msvc { .. } => "-W4",
+            ToolFamily::Gnu | ToolFamily::Clang => "-Wall",
+        }
+    }
+
+    /// What the flags to enable extra warnings
+    fn extra_warnings_flags(&self) -> Option<&'static str> {
+        match *self {
+            ToolFamily::Msvc { .. } => None,
+            ToolFamily::Gnu | ToolFamily::Clang => Some("-Wextra"),
+        }
+    }
+
+    /// What the flag to turn warning into errors
+    fn warnings_to_errors_flag(&self) -> &'static str {
+        match *self {
+            ToolFamily::Msvc { .. } => "-WX",
+            ToolFamily::Gnu | ToolFamily::Clang => "-Werror",
+        }
+    }
+
+    fn verbose_stderr(&self) -> bool {
+        *self == ToolFamily::Clang
+    }
+}
+
+/// Represents an object.
+///
+/// This is a source file -> object file pair.
+#[derive(Clone, Debug)]
+struct Object {
+    src: PathBuf,
+    dst: PathBuf,
+}
+
+impl Object {
+    /// Create a new source file -> object file pair.
+    fn new(src: PathBuf, dst: PathBuf) -> Object {
+        Object { src: src, dst: dst }
+    }
+}
+
+impl Build {
+    /// Construct a new instance of a blank set of configuration.
+    ///
+    /// This builder is finished with the [`compile`] function.
+    ///
+    /// [`compile`]: struct.Build.html#method.compile
+    pub fn new() -> Build {
+        Build {
+            include_directories: Vec::new(),
+            definitions: Vec::new(),
+            objects: Vec::new(),
+            flags: Vec::new(),
+            flags_supported: Vec::new(),
+            known_flag_support_status: Arc::new(Mutex::new(HashMap::new())),
+            ar_flags: Vec::new(),
+            no_default_flags: false,
+            files: Vec::new(),
+            shared_flag: None,
+            static_flag: None,
+            cpp: false,
+            cpp_link_stdlib: None,
+            cpp_set_stdlib: None,
+            cuda: false,
+            cudart: None,
+            target: None,
+            host: None,
+            out_dir: None,
+            opt_level: None,
+            debug: None,
+            force_frame_pointer: None,
+            env: Vec::new(),
+            compiler: None,
+            archiver: None,
+            cargo_metadata: true,
+            pic: None,
+            use_plt: None,
+            static_crt: None,
+            warnings: None,
+            extra_warnings: None,
+            warnings_into_errors: false,
+            env_cache: Arc::new(Mutex::new(HashMap::new())),
+            apple_sdk_root_cache: Arc::new(Mutex::new(HashMap::new())),
+        }
+    }
+
+    /// Add a directory to the `-I` or include path for headers
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use std::path::Path;
+    ///
+    /// let library_path = Path::new("/path/to/library");
+    ///
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .include(library_path)
+    ///     .include("src")
+    ///     .compile("foo");
+    /// ```
+    pub fn include<P: AsRef<Path>>(&mut self, dir: P) -> &mut Build {
+        self.include_directories.push(dir.as_ref().to_path_buf());
+        self
+    }
+
+    /// Add multiple directories to the `-I` include path.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// # use std::path::Path;
+    /// # let condition = true;
+    /// #
+    /// let mut extra_dir = None;
+    /// if condition {
+    ///     extra_dir = Some(Path::new("/path/to"));
+    /// }
+    ///
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .includes(extra_dir)
+    ///     .compile("foo");
+    /// ```
+    pub fn includes<P>(&mut self, dirs: P) -> &mut Build
+    where
+        P: IntoIterator,
+        P::Item: AsRef<Path>,
+    {
+        for dir in dirs {
+            self.include(dir);
+        }
+        self
+    }
+
+    /// Specify a `-D` variable with an optional value.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .define("FOO", "BAR")
+    ///     .define("BAZ", None)
+    ///     .compile("foo");
+    /// ```
+    pub fn define<'a, V: Into<Option<&'a str>>>(&mut self, var: &str, val: V) -> &mut Build {
+        self.definitions
+            .push((var.to_string(), val.into().map(|s| s.to_string())));
+        self
+    }
+
+    /// Add an arbitrary object file to link in
+    pub fn object<P: AsRef<Path>>(&mut self, obj: P) -> &mut Build {
+        self.objects.push(obj.as_ref().to_path_buf());
+        self
+    }
+
+    /// Add an arbitrary flag to the invocation of the compiler
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .flag("-ffunction-sections")
+    ///     .compile("foo");
+    /// ```
+    pub fn flag(&mut self, flag: &str) -> &mut Build {
+        self.flags.push(flag.to_string());
+        self
+    }
+
+    /// Add a flag to the invocation of the ar
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .file("src/bar.c")
+    ///     .ar_flag("/NODEFAULTLIB:libc.dll")
+    ///     .compile("foo");
+    /// ```
+    pub fn ar_flag(&mut self, flag: &str) -> &mut Build {
+        self.ar_flags.push(flag.to_string());
+        self
+    }
+
+    fn ensure_check_file(&self) -> Result<PathBuf, Error> {
+        let out_dir = self.get_out_dir()?;
+        let src = if self.cuda {
+            assert!(self.cpp);
+            out_dir.join("flag_check.cu")
+        } else if self.cpp {
+            out_dir.join("flag_check.cpp")
+        } else {
+            out_dir.join("flag_check.c")
+        };
+
+        if !src.exists() {
+            let mut f = fs::File::create(&src)?;
+            write!(f, "int main(void) {{ return 0; }}")?;
+        }
+
+        Ok(src)
+    }
+
+    /// Run the compiler to test if it accepts the given flag.
+    ///
+    /// For a convenience method for setting flags conditionally,
+    /// see `flag_if_supported()`.
+    ///
+    /// It may return error if it's unable to run the compiler with a test file
+    /// (e.g. the compiler is missing or a write to the `out_dir` failed).
+    ///
+    /// Note: Once computed, the result of this call is stored in the
+    /// `known_flag_support` field. If `is_flag_supported(flag)`
+    /// is called again, the result will be read from the hash table.
+    pub fn is_flag_supported(&self, flag: &str) -> Result<bool, Error> {
+        let mut known_status = self.known_flag_support_status.lock().unwrap();
+        if let Some(is_supported) = known_status.get(flag).cloned() {
+            return Ok(is_supported);
+        }
+
+        let out_dir = self.get_out_dir()?;
+        let src = self.ensure_check_file()?;
+        let obj = out_dir.join("flag_check");
+        let target = self.get_target()?;
+        let host = self.get_host()?;
+        let mut cfg = Build::new();
+        cfg.flag(flag)
+            .target(&target)
+            .opt_level(0)
+            .host(&host)
+            .debug(false)
+            .cpp(self.cpp)
+            .cuda(self.cuda);
+        let mut compiler = cfg.try_get_compiler()?;
+
+        // Clang uses stderr for verbose output, which yields a false positive
+        // result if the CFLAGS/CXXFLAGS include -v to aid in debugging.
+        if compiler.family.verbose_stderr() {
+            compiler.remove_arg("-v".into());
+        }
+
+        let mut cmd = compiler.to_command();
+        let is_arm = target.contains("aarch64") || target.contains("arm");
+        let clang = compiler.family == ToolFamily::Clang;
+        command_add_output_file(
+            &mut cmd,
+            &obj,
+            self.cuda,
+            target.contains("msvc"),
+            clang,
+            false,
+            is_arm,
+        );
+
+        // We need to explicitly tell msvc not to link and create an exe
+        // in the root directory of the crate
+        if target.contains("msvc") && !self.cuda {
+            cmd.arg("-c");
+        }
+
+        cmd.arg(&src);
+
+        let output = cmd.output()?;
+        let is_supported = output.stderr.is_empty();
+
+        known_status.insert(flag.to_owned(), is_supported);
+        Ok(is_supported)
+    }
+
+    /// Add an arbitrary flag to the invocation of the compiler if it supports it
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .flag_if_supported("-Wlogical-op") // only supported by GCC
+    ///     .flag_if_supported("-Wunreachable-code") // only supported by clang
+    ///     .compile("foo");
+    /// ```
+    pub fn flag_if_supported(&mut self, flag: &str) -> &mut Build {
+        self.flags_supported.push(flag.to_string());
+        self
+    }
+
+    /// Set the `-shared` flag.
+    ///
+    /// When enabled, the compiler will produce a shared object which can
+    /// then be linked with other objects to form an executable.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .shared_flag(true)
+    ///     .compile("libfoo.so");
+    /// ```
+    pub fn shared_flag(&mut self, shared_flag: bool) -> &mut Build {
+        self.shared_flag = Some(shared_flag);
+        self
+    }
+
+    /// Set the `-static` flag.
+    ///
+    /// When enabled on systems that support dynamic linking, this prevents
+    /// linking with the shared libraries.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .shared_flag(true)
+    ///     .static_flag(true)
+    ///     .compile("foo");
+    /// ```
+    pub fn static_flag(&mut self, static_flag: bool) -> &mut Build {
+        self.static_flag = Some(static_flag);
+        self
+    }
+
+    /// Disables the generation of default compiler flags. The default compiler
+    /// flags may cause conflicts in some cross compiling scenarios.
+    ///
+    /// Setting the `CRATE_CC_NO_DEFAULTS` environment variable has the same
+    /// effect as setting this to `true`. The presence of the environment
+    /// variable and the value of `no_default_flags` will be OR'd together.
+    pub fn no_default_flags(&mut self, no_default_flags: bool) -> &mut Build {
+        self.no_default_flags = no_default_flags;
+        self
+    }
+
+    /// Add a file which will be compiled
+    pub fn file<P: AsRef<Path>>(&mut self, p: P) -> &mut Build {
+        self.files.push(p.as_ref().to_path_buf());
+        self
+    }
+
+    /// Add files which will be compiled
+    pub fn files<P>(&mut self, p: P) -> &mut Build
+    where
+        P: IntoIterator,
+        P::Item: AsRef<Path>,
+    {
+        for file in p.into_iter() {
+            self.file(file);
+        }
+        self
+    }
+
+    /// Set C++ support.
+    ///
+    /// The other `cpp_*` options will only become active if this is set to
+    /// `true`.
+    pub fn cpp(&mut self, cpp: bool) -> &mut Build {
+        self.cpp = cpp;
+        self
+    }
+
+    /// Set CUDA C++ support.
+    ///
+    /// Enabling CUDA will pass the detected C/C++ toolchain as an argument to
+    /// the CUDA compiler, NVCC. NVCC itself accepts some limited GNU-like args;
+    /// any other arguments for the C/C++ toolchain will be redirected using
+    /// "-Xcompiler" flags.
+    ///
+    /// If enabled, this also implicitly enables C++ support.
+    pub fn cuda(&mut self, cuda: bool) -> &mut Build {
+        self.cuda = cuda;
+        if cuda {
+            self.cpp = true;
+            self.cudart = Some("static".to_string());
+        }
+        self
+    }
+
+    /// Link CUDA run-time.
+    ///
+    /// This option mimics the `--cudart` NVCC command-line option. Just like
+    /// the original it accepts `{none|shared|static}`, with default being
+    /// `static`. The method has to be invoked after `.cuda(true)`, or not
+    /// at all, if the default is right for the project.
+    pub fn cudart(&mut self, cudart: &str) -> &mut Build {
+        if self.cuda {
+            self.cudart = Some(cudart.to_string());
+        }
+        self
+    }
+
+    /// Set warnings into errors flag.
+    ///
+    /// Disabled by default.
+    ///
+    /// Warning: turning warnings into errors only make sense
+    /// if you are a developer of the crate using cc-rs.
+    /// Some warnings only appear on some architecture or
+    /// specific version of the compiler. Any user of this crate,
+    /// or any other crate depending on it, could fail during
+    /// compile time.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .warnings_into_errors(true)
+    ///     .compile("libfoo.a");
+    /// ```
+    pub fn warnings_into_errors(&mut self, warnings_into_errors: bool) -> &mut Build {
+        self.warnings_into_errors = warnings_into_errors;
+        self
+    }
+
+    /// Set warnings flags.
+    ///
+    /// Adds some flags:
+    /// - "-Wall" for MSVC.
+    /// - "-Wall", "-Wextra" for GNU and Clang.
+    ///
+    /// Enabled by default.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .warnings(false)
+    ///     .compile("libfoo.a");
+    /// ```
+    pub fn warnings(&mut self, warnings: bool) -> &mut Build {
+        self.warnings = Some(warnings);
+        self.extra_warnings = Some(warnings);
+        self
+    }
+
+    /// Set extra warnings flags.
+    ///
+    /// Adds some flags:
+    /// - nothing for MSVC.
+    /// - "-Wextra" for GNU and Clang.
+    ///
+    /// Enabled by default.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// // Disables -Wextra, -Wall remains enabled:
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .extra_warnings(false)
+    ///     .compile("libfoo.a");
+    /// ```
+    pub fn extra_warnings(&mut self, warnings: bool) -> &mut Build {
+        self.extra_warnings = Some(warnings);
+        self
+    }
+
+    /// Set the standard library to link against when compiling with C++
+    /// support.
+    ///
+    /// See [`get_cpp_link_stdlib`](cc::Build::get_cpp_link_stdlib) documentation
+    /// for the default value.
+    /// If the `CXXSTDLIB` environment variable is set, its value will
+    /// override the default value, but not the value explicitly set by calling
+    /// this function.
+    ///
+    /// A value of `None` indicates that no automatic linking should happen,
+    /// otherwise cargo will link against the specified library.
+    ///
+    /// The given library name must not contain the `lib` prefix.
+    ///
+    /// Common values:
+    /// - `stdc++` for GNU
+    /// - `c++` for Clang
+    /// - `c++_shared` or `c++_static` for Android
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .shared_flag(true)
+    ///     .cpp_link_stdlib("stdc++")
+    ///     .compile("libfoo.so");
+    /// ```
+    pub fn cpp_link_stdlib<'a, V: Into<Option<&'a str>>>(
+        &mut self,
+        cpp_link_stdlib: V,
+    ) -> &mut Build {
+        self.cpp_link_stdlib = Some(cpp_link_stdlib.into().map(|s| s.into()));
+        self
+    }
+
+    /// Force the C++ compiler to use the specified standard library.
+    ///
+    /// Setting this option will automatically set `cpp_link_stdlib` to the same
+    /// value.
+    ///
+    /// The default value of this option is always `None`.
+    ///
+    /// This option has no effect when compiling for a Visual Studio based
+    /// target.
+    ///
+    /// This option sets the `-stdlib` flag, which is only supported by some
+    /// compilers (clang, icc) but not by others (gcc). The library will not
+    /// detect which compiler is used, as such it is the responsibility of the
+    /// caller to ensure that this option is only used in conjunction with a
+    /// compiler which supports the `-stdlib` flag.
+    ///
+    /// A value of `None` indicates that no specific C++ standard library should
+    /// be used, otherwise `-stdlib` is added to the compile invocation.
+    ///
+    /// The given library name must not contain the `lib` prefix.
+    ///
+    /// Common values:
+    /// - `stdc++` for GNU
+    /// - `c++` for Clang
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .cpp_set_stdlib("c++")
+    ///     .compile("libfoo.a");
+    /// ```
+    pub fn cpp_set_stdlib<'a, V: Into<Option<&'a str>>>(
+        &mut self,
+        cpp_set_stdlib: V,
+    ) -> &mut Build {
+        let cpp_set_stdlib = cpp_set_stdlib.into();
+        self.cpp_set_stdlib = cpp_set_stdlib.map(|s| s.into());
+        self.cpp_link_stdlib(cpp_set_stdlib);
+        self
+    }
+
+    /// Configures the target this configuration will be compiling for.
+    ///
+    /// This option is automatically scraped from the `TARGET` environment
+    /// variable by build scripts, so it's not required to call this function.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .target("aarch64-linux-android")
+    ///     .compile("foo");
+    /// ```
+    pub fn target(&mut self, target: &str) -> &mut Build {
+        self.target = Some(target.to_string());
+        self
+    }
+
+    /// Configures the host assumed by this configuration.
+    ///
+    /// This option is automatically scraped from the `HOST` environment
+    /// variable by build scripts, so it's not required to call this function.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// cc::Build::new()
+    ///     .file("src/foo.c")
+    ///     .host("arm-linux-gnueabihf")
+    ///     .compile("foo");
+    /// ```
+    pub fn host(&mut self, host: &str) -> &mut Build {
+        self.host = Some(host.to_string());
+        self
+    }
+
+    /// Configures the optimization level of the generated object files.
+    ///
+    /// This option is automatically scraped from the `OPT_LEVEL` environment
+    /// variable by build scripts, so it's not required to call this function.
+    pub fn opt_level(&mut self, opt_level: u32) -> &mut Build {
+        self.opt_level = Some(opt_level.to_string());
+        self
+    }
+
+    /// Configures the optimization level of the generated object files.
+    ///
+    /// This option is automatically scraped from the `OPT_LEVEL` environment
+    /// variable by build scripts, so it's not required to call this function.
+    pub fn opt_level_str(&mut self, opt_level: &str) -> &mut Build {
+        self.opt_level = Some(opt_level.to_string());
+        self
+    }
+
+    /// Configures whether the compiler will emit debug information when
+    /// generating object files.
+    ///
+    /// This option is automatically scraped from the `DEBUG` environment
+    /// variable by build scripts, so it's not required to call this function.
+    pub fn debug(&mut self, debug: bool) -> &mut Build {
+        self.debug = Some(debug);
+        self
+    }
+
+    /// Configures whether the compiler will emit instructions to store
+    /// frame pointers during codegen.
+    ///
+    /// This option is automatically enabled when debug information is emitted.
+    /// Otherwise the target platform compiler's default will be used.
+    /// You can use this option to force a specific setting.
+    pub fn force_frame_pointer(&mut self, force: bool) -> &mut Build {
+        self.force_frame_pointer = Some(force);
+        self
+    }
+
+    /// Configures the output directory where all object files and static
+    /// libraries will be located.
+    ///
+    /// This option is automatically scraped from the `OUT_DIR` environment
+    /// variable by build scripts, so it's not required to call this function.
+    pub fn out_dir<P: AsRef<Path>>(&mut self, out_dir: P) -> &mut Build {
+        self.out_dir = Some(out_dir.as_ref().to_owned());
+        self
+    }
+
+    /// Configures the compiler to be used to produce output.
+    ///
+    /// This option is automatically determined from the target platform or a
+    /// number of environment variables, so it's not required to call this
+    /// function.
+    pub fn compiler<P: AsRef<Path>>(&mut self, compiler: P) -> &mut Build {
+        self.compiler = Some(compiler.as_ref().to_owned());
+        self
+    }
+
+    /// Configures the tool used to assemble archives.
+    ///
+    /// This option is automatically determined from the target platform or a
+    /// number of environment variables, so it's not required to call this
+    /// function.
+    pub fn archiver<P: AsRef<Path>>(&mut self, archiver: P) -> &mut Build {
+        self.archiver = Some(archiver.as_ref().to_owned());
+        self
+    }
+    /// Define whether metadata should be emitted for cargo allowing it to
+    /// automatically link the binary. Defaults to `true`.
+    ///
+    /// The emitted metadata is:
+    ///
+    ///  - `rustc-link-lib=static=`*compiled lib*
+    ///  - `rustc-link-search=native=`*target folder*
+    ///  - When target is MSVC, the ATL-MFC libs are added via `rustc-link-search=native=`
+    ///  - When C++ is enabled, the C++ stdlib is added via `rustc-link-lib`
+    ///
+    pub fn cargo_metadata(&mut self, cargo_metadata: bool) -> &mut Build {
+        self.cargo_metadata = cargo_metadata;
+        self
+    }
+
+    /// Configures whether the compiler will emit position independent code.
+    ///
+    /// This option defaults to `false` for `windows-gnu` and bare metal targets and
+    /// to `true` for all other targets.
+    pub fn pic(&mut self, pic: bool) -> &mut Build {
+        self.pic = Some(pic);
+        self
+    }
+
+    /// Configures whether the Procedure Linkage Table is used for indirect
+    /// calls into shared libraries.
+    ///
+    /// The PLT is used to provide features like lazy binding, but introduces
+    /// a small performance loss due to extra pointer indirection. Setting
+    /// `use_plt` to `false` can provide a small performance increase.
+    ///
+    /// Note that skipping the PLT requires a recent version of GCC/Clang.
+    ///
+    /// This only applies to ELF targets. It has no effect on other platforms.
+    pub fn use_plt(&mut self, use_plt: bool) -> &mut Build {
+        self.use_plt = Some(use_plt);
+        self
+    }
+
+    /// Configures whether the /MT flag or the /MD flag will be passed to msvc build tools.
+    ///
+    /// This option defaults to `false`, and affect only msvc targets.
+    pub fn static_crt(&mut self, static_crt: bool) -> &mut Build {
+        self.static_crt = Some(static_crt);
+        self
+    }
+
+    #[doc(hidden)]
+    pub fn __set_env<A, B>(&mut self, a: A, b: B) -> &mut Build
+    where
+        A: AsRef<OsStr>,
+        B: AsRef<OsStr>,
+    {
+        self.env
+            .push((a.as_ref().to_owned(), b.as_ref().to_owned()));
+        self
+    }
+
+    /// Run the compiler, generating the file `output`
+    ///
+    /// This will return a result instead of panicing; see compile() for the complete description.
+    pub fn try_compile(&self, output: &str) -> Result<(), Error> {
+        let mut output_components = Path::new(output).components();
+        match (output_components.next(), output_components.next()) {
+            (Some(Component::Normal(_)), None) => {}
+            _ => {
+                return Err(Error::new(
+                    ErrorKind::InvalidArgument,
+                    "argument of `compile` must be a single normal path component",
+                ));
+            }
+        }
+
+        let (lib_name, gnu_lib_name) = if output.starts_with("lib") && output.ends_with(".a") {
+            (&output[3..output.len() - 2], output.to_owned())
+        } else {
+            let mut gnu = String::with_capacity(5 + output.len());
+            gnu.push_str("lib");
+            gnu.push_str(&output);
+            gnu.push_str(".a");
+            (output, gnu)
+        };
+        let dst = self.get_out_dir()?;
+
+        let mut objects = Vec::new();
+        for file in self.files.iter() {
+            let obj = dst.join(file).with_extension("o");
+            let obj = if !obj.starts_with(&dst) {
+                dst.join(obj.file_name().ok_or_else(|| {
+                    Error::new(ErrorKind::IOError, "Getting object file details failed.")
+                })?)
+            } else {
+                obj
+            };
+
+            match obj.parent() {
+                Some(s) => fs::create_dir_all(s)?,
+                None => {
+                    return Err(Error::new(
+                        ErrorKind::IOError,
+                        "Getting object file details failed.",
+                    ));
+                }
+            };
+
+            objects.push(Object::new(file.to_path_buf(), obj));
+        }
+        self.compile_objects(&objects)?;
+        self.assemble(lib_name, &dst.join(gnu_lib_name), &objects)?;
+
+        if self.get_target()?.contains("msvc") {
+            let compiler = self.get_base_compiler()?;
+            let atlmfc_lib = compiler
+                .env()
+                .iter()
+                .find(|&&(ref var, _)| var.as_os_str() == OsStr::new("LIB"))
+                .and_then(|&(_, ref lib_paths)| {
+                    env::split_paths(lib_paths).find(|path| {
+                        let sub = Path::new("atlmfc/lib");
+                        path.ends_with(sub) || path.parent().map_or(false, |p| p.ends_with(sub))
+                    })
+                });
+
+            if let Some(atlmfc_lib) = atlmfc_lib {
+                self.print(&format!(
+                    "cargo:rustc-link-search=native={}",
+                    atlmfc_lib.display()
+                ));
+            }
+        }
+
+        self.print(&format!("cargo:rustc-link-lib=static={}", lib_name));
+        self.print(&format!("cargo:rustc-link-search=native={}", dst.display()));
+
+        // Add specific C++ libraries, if enabled.
+        if self.cpp {
+            if let Some(stdlib) = self.get_cpp_link_stdlib()? {
+                self.print(&format!("cargo:rustc-link-lib={}", stdlib));
+            }
+        }
+
+        let cudart = match &self.cudart {
+            Some(opt) => opt.as_str(), // {none|shared|static}
+            None => "none",
+        };
+        if cudart != "none" {
+            if let Some(nvcc) = which(&self.get_compiler().path) {
+                // Try to figure out the -L search path. If it fails,
+                // it's on user to specify one by passing it through
+                // RUSTFLAGS environment variable.
+                let mut libtst = false;
+                let mut libdir = nvcc;
+                libdir.pop(); // remove 'nvcc'
+                libdir.push("..");
+                let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
+                if cfg!(target_os = "linux") {
+                    libdir.push("targets");
+                    libdir.push(target_arch.to_owned() + "-linux");
+                    libdir.push("lib");
+                    libtst = true;
+                } else if cfg!(target_env = "msvc") {
+                    libdir.push("lib");
+                    match target_arch.as_str() {
+                        "x86_64" => {
+                            libdir.push("x64");
+                            libtst = true;
+                        }
+                        "x86" => {
+                            libdir.push("Win32");
+                            libtst = true;
+                        }
+                        _ => libtst = false,
+                    }
+                }
+                if libtst && libdir.is_dir() {
+                    println!(
+                        "cargo:rustc-link-search=native={}",
+                        libdir.to_str().unwrap()
+                    );
+                }
+
+                // And now the -l flag.
+                let lib = match cudart {
+                    "shared" => "cudart",
+                    "static" => "cudart_static",
+                    bad => panic!("unsupported cudart option: {}", bad),
+                };
+                println!("cargo:rustc-link-lib={}", lib);
+            }
+        }
+
+        Ok(())
+    }
+
+    /// Run the compiler, generating the file `output`
+    ///
+    /// # Library name
+    ///
+    /// The `output` string argument determines the file name for the compiled
+    /// library. The Rust compiler will create an assembly named "lib"+output+".a".
+    /// MSVC will create a file named output+".lib".
+    ///
+    /// The choice of `output` is close to arbitrary, but:
+    ///
+    /// - must be nonempty,
+    /// - must not contain a path separator (`/`),
+    /// - must be unique across all `compile` invocations made by the same build
+    ///   script.
+    ///
+    /// If your build script compiles a single source file, the base name of
+    /// that source file would usually be reasonable:
+    ///
+    /// ```no_run
+    /// cc::Build::new().file("blobstore.c").compile("blobstore");
+    /// ```
+    ///
+    /// Compiling multiple source files, some people use their crate's name, or
+    /// their crate's name + "-cc".
+    ///
+    /// Otherwise, please use your imagination.
+    ///
+    /// For backwards compatibility, if `output` starts with "lib" *and* ends
+    /// with ".a", a second "lib" prefix and ".a" suffix do not get added on,
+    /// but this usage is deprecated; please omit `lib` and `.a` in the argument
+    /// that you pass.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `output` is not formatted correctly or if one of the underlying
+    /// compiler commands fails. It can also panic if it fails reading file names
+    /// or creating directories.
+    pub fn compile(&self, output: &str) {
+        if let Err(e) = self.try_compile(output) {
+            fail(&e.message);
+        }
+    }
+
+    #[cfg(feature = "parallel")]
+    fn compile_objects<'me>(&'me self, objs: &[Object]) -> Result<(), Error> {
+        use std::sync::atomic::{AtomicBool, Ordering::SeqCst};
+        use std::sync::Once;
+
+        // Limit our parallelism globally with a jobserver. Start off by
+        // releasing our own token for this process so we can have a bit of an
+        // easier to write loop below. If this fails, though, then we're likely
+        // on Windows with the main implicit token, so we just have a bit extra
+        // parallelism for a bit and don't reacquire later.
+        let server = jobserver();
+        let reacquire = server.release_raw().is_ok();
+
+        // When compiling objects in parallel we do a few dirty tricks to speed
+        // things up:
+        //
+        // * First is that we use the `jobserver` crate to limit the parallelism
+        //   of this build script. The `jobserver` crate will use a jobserver
+        //   configured by Cargo for build scripts to ensure that parallelism is
+        //   coordinated across C compilations and Rust compilations. Before we
+        //   compile anything we make sure to wait until we acquire a token.
+        //
+        //   Note that this jobserver is cached globally so we only used one per
+        //   process and only worry about creating it once.
+        //
+        // * Next we use a raw `thread::spawn` per thread to actually compile
+        //   objects in parallel. We only actually spawn a thread after we've
+        //   acquired a token to perform some work
+        //
+        // * Finally though we want to keep the dependencies of this crate
+        //   pretty light, so we avoid using a safe abstraction like `rayon` and
+        //   instead rely on some bits of `unsafe` code. We know that this stack
+        //   frame persists while everything is compiling so we use all the
+        //   stack-allocated objects without cloning/reallocating. We use a
+        //   transmute to `State` with a `'static` lifetime to persist
+        //   everything we need across the boundary, and the join-on-drop
+        //   semantics of `JoinOnDrop` should ensure that our stack frame is
+        //   alive while threads are alive.
+        //
+        // With all that in mind we compile all objects in a loop here, after we
+        // acquire the appropriate tokens, Once all objects have been compiled
+        // we join on all the threads and propagate the results of compilation.
+        //
+        // Note that as a slight optimization we try to break out as soon as
+        // possible as soon as any compilation fails to ensure that errors get
+        // out to the user as fast as possible.
+        let error = AtomicBool::new(false);
+        let mut threads = Vec::new();
+        for obj in objs {
+            if error.load(SeqCst) {
+                break;
+            }
+            let token = server.acquire()?;
+            let state = State {
+                build: self,
+                obj,
+                error: &error,
+            };
+            let state = unsafe { std::mem::transmute::<State, State<'static>>(state) };
+            let thread = thread::spawn(|| {
+                let state: State<'me> = state; // erase the `'static` lifetime
+                let result = state.build.compile_object(state.obj);
+                if result.is_err() {
+                    state.error.store(true, SeqCst);
+                }
+                drop(token); // make sure our jobserver token is released after the compile
+                return result;
+            });
+            threads.push(JoinOnDrop(Some(thread)));
+        }
+
+        for mut thread in threads {
+            if let Some(thread) = thread.0.take() {
+                thread.join().expect("thread should not panic")?;
+            }
+        }
+
+        // Reacquire our process's token before we proceed, which we released
+        // before entering the loop above.
+        if reacquire {
+            server.acquire_raw()?;
+        }
+
+        return Ok(());
+
+        /// Shared state from the parent thread to the child thread. This
+        /// package of pointers is temporarily transmuted to a `'static`
+        /// lifetime to cross the thread boundary and then once the thread is
+        /// running we erase the `'static` to go back to an anonymous lifetime.
+        struct State<'a> {
+            build: &'a Build,
+            obj: &'a Object,
+            error: &'a AtomicBool,
+        }
+
+        /// Returns a suitable `jobserver::Client` used to coordinate
+        /// parallelism between build scripts.
+        fn jobserver() -> &'static jobserver::Client {
+            static INIT: Once = Once::new();
+            static mut JOBSERVER: Option<jobserver::Client> = None;
+
+            fn _assert_sync<T: Sync>() {}
+            _assert_sync::<jobserver::Client>();
+
+            unsafe {
+                INIT.call_once(|| {
+                    let server = default_jobserver();
+                    JOBSERVER = Some(server);
+                });
+                JOBSERVER.as_ref().unwrap()
+            }
+        }
+
+        unsafe fn default_jobserver() -> jobserver::Client {
+            // Try to use the environmental jobserver which Cargo typically
+            // initializes for us...
+            if let Some(client) = jobserver::Client::from_env() {
+                return client;
+            }
+
+            // ... but if that fails for whatever reason select something
+            // reasonable and crate a new jobserver. Use `NUM_JOBS` if set (it's
+            // configured by Cargo) and otherwise just fall back to a
+            // semi-reasonable number. Note that we could use `num_cpus` here
+            // but it's an extra dependency that will almost never be used, so
+            // it's generally not too worth it.
+            let mut parallelism = 4;
+            if let Ok(amt) = env::var("NUM_JOBS") {
+                if let Ok(amt) = amt.parse() {
+                    parallelism = amt;
+                }
+            }
+
+            // If we create our own jobserver then be sure to reserve one token
+            // for ourselves.
+            let client = jobserver::Client::new(parallelism).expect("failed to create jobserver");
+            client.acquire_raw().expect("failed to acquire initial");
+            return client;
+        }
+
+        struct JoinOnDrop(Option<thread::JoinHandle<Result<(), Error>>>);
+
+        impl Drop for JoinOnDrop {
+            fn drop(&mut self) {
+                if let Some(thread) = self.0.take() {
+                    drop(thread.join());
+                }
+            }
+        }
+    }
+
+    #[cfg(not(feature = "parallel"))]
+    fn compile_objects(&self, objs: &[Object]) -> Result<(), Error> {
+        for obj in objs {
+            self.compile_object(obj)?;
+        }
+        Ok(())
+    }
+
+    fn compile_object(&self, obj: &Object) -> Result<(), Error> {
+        let is_asm = obj.src.extension().and_then(|s| s.to_str()) == Some("asm");
+        let target = self.get_target()?;
+        let msvc = target.contains("msvc");
+        let compiler = self.try_get_compiler()?;
+        let clang = compiler.family == ToolFamily::Clang;
+        let (mut cmd, name) = if msvc && is_asm {
+            self.msvc_macro_assembler()?
+        } else {
+            let mut cmd = compiler.to_command();
+            for &(ref a, ref b) in self.env.iter() {
+                cmd.env(a, b);
+            }
+            (
+                cmd,
+                compiler
+                    .path
+                    .file_name()
+                    .ok_or_else(|| Error::new(ErrorKind::IOError, "Failed to get compiler path."))?
+                    .to_string_lossy()
+                    .into_owned(),
+            )
+        };
+        let is_arm = target.contains("aarch64") || target.contains("arm");
+        command_add_output_file(&mut cmd, &obj.dst, self.cuda, msvc, clang, is_asm, is_arm);
+        // armasm and armasm64 don't requrie -c option
+        if !msvc || !is_asm || !is_arm {
+            cmd.arg("-c");
+        }
+        if self.cuda && self.files.len() > 1 {
+            cmd.arg("--device-c");
+        }
+        cmd.arg(&obj.src);
+        if cfg!(target_os = "macos") {
+            self.fix_env_for_apple_os(&mut cmd)?;
+        }
+
+        run(&mut cmd, &name)?;
+        Ok(())
+    }
+
+    /// This will return a result instead of panicing; see expand() for the complete description.
+    pub fn try_expand(&self) -> Result<Vec<u8>, Error> {
+        let compiler = self.try_get_compiler()?;
+        let mut cmd = compiler.to_command();
+        for &(ref a, ref b) in self.env.iter() {
+            cmd.env(a, b);
+        }
+        cmd.arg("-E");
+
+        assert!(
+            self.files.len() <= 1,
+            "Expand may only be called for a single file"
+        );
+
+        for file in self.files.iter() {
+            cmd.arg(file);
+        }
+
+        let name = compiler
+            .path
+            .file_name()
+            .ok_or_else(|| Error::new(ErrorKind::IOError, "Failed to get compiler path."))?
+            .to_string_lossy()
+            .into_owned();
+
+        Ok(run_output(&mut cmd, &name)?)
+    }
+
+    /// Run the compiler, returning the macro-expanded version of the input files.
+    ///
+    /// This is only relevant for C and C++ files.
+    ///
+    /// # Panics
+    /// Panics if more than one file is present in the config, or if compiler
+    /// path has an invalid file name.
+    ///
+    /// # Example
+    /// ```no_run
+    /// let out = cc::Build::new().file("src/foo.c").expand();
+    /// ```
+    pub fn expand(&self) -> Vec<u8> {
+        match self.try_expand() {
+            Err(e) => fail(&e.message),
+            Ok(v) => v,
+        }
+    }
+
+    /// Get the compiler that's in use for this configuration.
+    ///
+    /// This function will return a `Tool` which represents the culmination
+    /// of this configuration at a snapshot in time. The returned compiler can
+    /// be inspected (e.g. the path, arguments, environment) to forward along to
+    /// other tools, or the `to_command` method can be used to invoke the
+    /// compiler itself.
+    ///
+    /// This method will take into account all configuration such as debug
+    /// information, optimization level, include directories, defines, etc.
+    /// Additionally, the compiler binary in use follows the standard
+    /// conventions for this path, e.g. looking at the explicitly set compiler,
+    /// environment variables (a number of which are inspected here), and then
+    /// falling back to the default configuration.
+    ///
+    /// # Panics
+    ///
+    /// Panics if an error occurred while determining the architecture.
+    pub fn get_compiler(&self) -> Tool {
+        match self.try_get_compiler() {
+            Ok(tool) => tool,
+            Err(e) => fail(&e.message),
+        }
+    }
+
+    /// Get the compiler that's in use for this configuration.
+    ///
+    /// This will return a result instead of panicing; see get_compiler() for the complete description.
+    pub fn try_get_compiler(&self) -> Result<Tool, Error> {
+        let opt_level = self.get_opt_level()?;
+        let target = self.get_target()?;
+
+        let mut cmd = self.get_base_compiler()?;
+        let envflags = self.envflags(if self.cpp { "CXXFLAGS" } else { "CFLAGS" });
+
+        // Disable default flag generation via `no_default_flags` or environment variable
+        let no_defaults = self.no_default_flags || self.getenv("CRATE_CC_NO_DEFAULTS").is_some();
+
+        if !no_defaults {
+            self.add_default_flags(&mut cmd, &target, &opt_level)?;
+        } else {
+            println!("Info: default compiler flags are disabled");
+        }
+
+        for arg in envflags {
+            cmd.push_cc_arg(arg.into());
+        }
+
+        for directory in self.include_directories.iter() {
+            cmd.args.push("-I".into());
+            cmd.args.push(directory.into());
+        }
+
+        // If warnings and/or extra_warnings haven't been explicitly set,
+        // then we set them only if the environment doesn't already have
+        // CFLAGS/CXXFLAGS, since those variables presumably already contain
+        // the desired set of warnings flags.
+
+        if self
+            .warnings
+            .unwrap_or(if self.has_flags() { false } else { true })
+        {
+            let wflags = cmd.family.warnings_flags().into();
+            cmd.push_cc_arg(wflags);
+        }
+
+        if self
+            .extra_warnings
+            .unwrap_or(if self.has_flags() { false } else { true })
+        {
+            if let Some(wflags) = cmd.family.extra_warnings_flags() {
+                cmd.push_cc_arg(wflags.into());
+            }
+        }
+
+        for flag in self.flags.iter() {
+            cmd.args.push(flag.into());
+        }
+
+        for flag in self.flags_supported.iter() {
+            if self.is_flag_supported(flag).unwrap_or(false) {
+                cmd.push_cc_arg(flag.into());
+            }
+        }
+
+        for &(ref key, ref value) in self.definitions.iter() {
+            if let Some(ref value) = *value {
+                cmd.args.push(format!("-D{}={}", key, value).into());
+            } else {
+                cmd.args.push(format!("-D{}", key).into());
+            }
+        }
+
+        if self.warnings_into_errors {
+            let warnings_to_errors_flag = cmd.family.warnings_to_errors_flag().into();
+            cmd.push_cc_arg(warnings_to_errors_flag);
+        }
+
+        Ok(cmd)
+    }
+
+    fn add_default_flags(
+        &self,
+        cmd: &mut Tool,
+        target: &str,
+        opt_level: &str,
+    ) -> Result<(), Error> {
+        // Non-target flags
+        // If the flag is not conditioned on target variable, it belongs here :)
+        match cmd.family {
+            ToolFamily::Msvc { .. } => {
+                cmd.push_cc_arg("-nologo".into());
+
+                let crt_flag = match self.static_crt {
+                    Some(true) => "-MT",
+                    Some(false) => "-MD",
+                    None => {
+                        let features = self
+                            .getenv("CARGO_CFG_TARGET_FEATURE")
+                            .unwrap_or(String::new());
+                        if features.contains("crt-static") {
+                            "-MT"
+                        } else {
+                            "-MD"
+                        }
+                    }
+                };
+                cmd.push_cc_arg(crt_flag.into());
+
+                match &opt_level[..] {
+                    // Msvc uses /O1 to enable all optimizations that minimize code size.
+                    "z" | "s" | "1" => cmd.push_opt_unless_duplicate("-O1".into()),
+                    // -O3 is a valid value for gcc and clang compilers, but not msvc. Cap to /O2.
+                    "2" | "3" => cmd.push_opt_unless_duplicate("-O2".into()),
+                    _ => {}
+                }
+            }
+            ToolFamily::Gnu | ToolFamily::Clang => {
+                // arm-linux-androideabi-gcc 4.8 shipped with Android NDK does
+                // not support '-Oz'
+                if opt_level == "z" && cmd.family != ToolFamily::Clang {
+                    cmd.push_opt_unless_duplicate("-Os".into());
+                } else {
+                    cmd.push_opt_unless_duplicate(format!("-O{}", opt_level).into());
+                }
+
+                if cmd.family == ToolFamily::Clang && target.contains("android") {
+                    // For compatibility with code that doesn't use pre-defined `__ANDROID__` macro.
+                    // If compiler used via ndk-build or cmake (officially supported build methods)
+                    // this macros is defined.
+                    // See https://android.googlesource.com/platform/ndk/+/refs/heads/ndk-release-r21/build/cmake/android.toolchain.cmake#456
+                    // https://android.googlesource.com/platform/ndk/+/refs/heads/ndk-release-r21/build/core/build-binary.mk#141
+                    cmd.push_opt_unless_duplicate("-DANDROID".into());
+                }
+
+                if !target.contains("apple-ios") {
+                    cmd.push_cc_arg("-ffunction-sections".into());
+                    cmd.push_cc_arg("-fdata-sections".into());
+                }
+                // Disable generation of PIC on bare-metal for now: rust-lld doesn't support this yet
+                if self.pic.unwrap_or(
+                    !target.contains("windows")
+                        && !target.contains("-none-")
+                        && !target.contains("uefi"),
+                ) {
+                    cmd.push_cc_arg("-fPIC".into());
+                    // PLT only applies if code is compiled with PIC support,
+                    // and only for ELF targets.
+                    if target.contains("linux") && !self.use_plt.unwrap_or(true) {
+                        cmd.push_cc_arg("-fno-plt".into());
+                    }
+                }
+            }
+        }
+
+        if self.get_debug() {
+            if self.cuda {
+                // NVCC debug flag
+                cmd.args.push("-G".into());
+            }
+            let family = cmd.family;
+            family.add_debug_flags(cmd);
+        }
+
+        if self.get_force_frame_pointer() {
+            let family = cmd.family;
+            family.add_force_frame_pointer(cmd);
+        }
+
+        // Target flags
+        match cmd.family {
+            ToolFamily::Clang => {
+                if !(target.contains("android")
+                    && android_clang_compiler_uses_target_arg_internally(&cmd.path))
+                {
+                    if target.contains("darwin") {
+                        if let Some(arch) =
+                            map_darwin_target_from_rust_to_compiler_architecture(target)
+                        {
+                            cmd.args
+                                .push(format!("--target={}-apple-darwin", arch).into());
+                        }
+                    } else if target.contains("macabi") {
+                        if let Some(arch) =
+                            map_darwin_target_from_rust_to_compiler_architecture(target)
+                        {
+                            cmd.args
+                                .push(format!("--target={}-apple-ios13.0-macabi", arch).into());
+                        }
+                    } else if target.contains("ios-sim") {
+                        if let Some(arch) =
+                            map_darwin_target_from_rust_to_compiler_architecture(target)
+                        {
+                            let deployment_target = env::var("IPHONEOS_DEPLOYMENT_TARGET")
+                                .unwrap_or_else(|_| "7.0".into());
+                            cmd.args.push(
+                                format!(
+                                    "--target={}-apple-ios{}-simulator",
+                                    arch, deployment_target
+                                )
+                                .into(),
+                            );
+                        }
+                    } else if target.starts_with("riscv64gc-") {
+                        cmd.args.push(
+                            format!("--target={}", target.replace("riscv64gc", "riscv64")).into(),
+                        );
+                    } else if target.starts_with("riscv32gc-") {
+                        cmd.args.push(
+                            format!("--target={}", target.replace("riscv32gc", "riscv32")).into(),
+                        );
+                    } else if target.contains("uefi") {
+                        if target.contains("x86_64") {
+                            cmd.args.push("--target=x86_64-unknown-windows-gnu".into());
+                        } else if target.contains("i686") {
+                            cmd.args.push("--target=i686-unknown-windows-gnu".into())
+                        } else if target.contains("aarch64") {
+                            cmd.args.push("--target=aarch64-unknown-windows-gnu".into())
+                        }
+                    } else {
+                        cmd.args.push(format!("--target={}", target).into());
+                    }
+                }
+            }
+            ToolFamily::Msvc { clang_cl } => {
+                // This is an undocumented flag from MSVC but helps with making
+                // builds more reproducible by avoiding putting timestamps into
+                // files.
+                cmd.push_cc_arg("-Brepro".into());
+
+                if clang_cl {
+                    if target.contains("x86_64") {
+                        cmd.push_cc_arg("-m64".into());
+                    } else if target.contains("86") {
+                        cmd.push_cc_arg("-m32".into());
+                        cmd.push_cc_arg("-arch:IA32".into());
+                    } else {
+                        cmd.push_cc_arg(format!("--target={}", target).into());
+                    }
+                } else {
+                    if target.contains("i586") {
+                        cmd.push_cc_arg("-arch:IA32".into());
+                    }
+                }
+
+                // There is a check in corecrt.h that will generate a
+                // compilation error if
+                // _ARM_WINAPI_PARTITION_DESKTOP_SDK_AVAILABLE is
+                // not defined to 1. The check was added in Windows
+                // 8 days because only store apps were allowed on ARM.
+                // This changed with the release of Windows 10 IoT Core.
+                // The check will be going away in future versions of
+                // the SDK, but for all released versions of the
+                // Windows SDK it is required.
+                if target.contains("arm") || target.contains("thumb") {
+                    cmd.args
+                        .push("-D_ARM_WINAPI_PARTITION_DESKTOP_SDK_AVAILABLE=1".into());
+                }
+            }
+            ToolFamily::Gnu => {
+                if target.contains("i686") || target.contains("i586") {
+                    cmd.args.push("-m32".into());
+                } else if target == "x86_64-unknown-linux-gnux32" {
+                    cmd.args.push("-mx32".into());
+                } else if target.contains("x86_64") || target.contains("powerpc64") {
+                    cmd.args.push("-m64".into());
+                }
+
+                if target.contains("darwin") {
+                    if let Some(arch) = map_darwin_target_from_rust_to_compiler_architecture(target)
+                    {
+                        cmd.args.push("-arch".into());
+                        cmd.args.push(arch.into());
+                    }
+                }
+
+                if target.contains("-kmc-solid_") {
+                    cmd.args.push("-finput-charset=utf-8".into());
+                }
+
+                if self.static_flag.is_none() {
+                    let features = self
+                        .getenv("CARGO_CFG_TARGET_FEATURE")
+                        .unwrap_or(String::new());
+                    if features.contains("crt-static") {
+                        cmd.args.push("-static".into());
+                    }
+                }
+
+                // armv7 targets get to use armv7 instructions
+                if (target.starts_with("armv7") || target.starts_with("thumbv7"))
+                    && (target.contains("-linux-") || target.contains("-kmc-solid_"))
+                {
+                    cmd.args.push("-march=armv7-a".into());
+
+                    if target.ends_with("eabihf") {
+                        // lowest common denominator FPU
+                        cmd.args.push("-mfpu=vfpv3-d16".into());
+                    }
+                }
+
+                // (x86 Android doesn't say "eabi")
+                if target.contains("-androideabi") && target.contains("v7") {
+                    // -march=armv7-a handled above
+                    cmd.args.push("-mthumb".into());
+                    if !target.contains("neon") {
+                        // On android we can guarantee some extra float instructions
+                        // (specified in the android spec online)
+                        // NEON guarantees even more; see below.
+                        cmd.args.push("-mfpu=vfpv3-d16".into());
+                    }
+                    cmd.args.push("-mfloat-abi=softfp".into());
+                }
+
+                if target.contains("neon") {
+                    cmd.args.push("-mfpu=neon-vfpv4".into());
+                }
+
+                if target.starts_with("armv4t-unknown-linux-") {
+                    cmd.args.push("-march=armv4t".into());
+                    cmd.args.push("-marm".into());
+                    cmd.args.push("-mfloat-abi=soft".into());
+                }
+
+                if target.starts_with("armv5te-unknown-linux-") {
+                    cmd.args.push("-march=armv5te".into());
+                    cmd.args.push("-marm".into());
+                    cmd.args.push("-mfloat-abi=soft".into());
+                }
+
+                // For us arm == armv6 by default
+                if target.starts_with("arm-unknown-linux-") {
+                    cmd.args.push("-march=armv6".into());
+                    cmd.args.push("-marm".into());
+                    if target.ends_with("hf") {
+                        cmd.args.push("-mfpu=vfp".into());
+                    } else {
+                        cmd.args.push("-mfloat-abi=soft".into());
+                    }
+                }
+
+                // We can guarantee some settings for FRC
+                if target.starts_with("arm-frc-") {
+                    cmd.args.push("-march=armv7-a".into());
+                    cmd.args.push("-mcpu=cortex-a9".into());
+                    cmd.args.push("-mfpu=vfpv3".into());
+                    cmd.args.push("-mfloat-abi=softfp".into());
+                    cmd.args.push("-marm".into());
+                }
+
+                // Turn codegen down on i586 to avoid some instructions.
+                if target.starts_with("i586-unknown-linux-") {
+                    cmd.args.push("-march=pentium".into());
+                }
+
+                // Set codegen level for i686 correctly
+                if target.starts_with("i686-unknown-linux-") {
+                    cmd.args.push("-march=i686".into());
+                }
+
+                // Looks like `musl-gcc` makes it hard for `-m32` to make its way
+                // all the way to the linker, so we need to actually instruct the
+                // linker that we're generating 32-bit executables as well. This'll
+                // typically only be used for build scripts which transitively use
+                // these flags that try to compile executables.
+                if target == "i686-unknown-linux-musl" || target == "i586-unknown-linux-musl" {
+                    cmd.args.push("-Wl,-melf_i386".into());
+                }
+
+                if target.starts_with("thumb") {
+                    cmd.args.push("-mthumb".into());
+
+                    if target.ends_with("eabihf") {
+                        cmd.args.push("-mfloat-abi=hard".into())
+                    }
+                }
+                if target.starts_with("thumbv6m") {
+                    cmd.args.push("-march=armv6s-m".into());
+                }
+                if target.starts_with("thumbv7em") {
+                    cmd.args.push("-march=armv7e-m".into());
+
+                    if target.ends_with("eabihf") {
+                        cmd.args.push("-mfpu=fpv4-sp-d16".into())
+                    }
+                }
+                if target.starts_with("thumbv7m") {
+                    cmd.args.push("-march=armv7-m".into());
+                }
+                if target.starts_with("thumbv8m.base") {
+                    cmd.args.push("-march=armv8-m.base".into());
+                }
+                if target.starts_with("thumbv8m.main") {
+                    cmd.args.push("-march=armv8-m.main".into());
+
+                    if target.ends_with("eabihf") {
+                        cmd.args.push("-mfpu=fpv5-sp-d16".into())
+                    }
+                }
+                if target.starts_with("armebv7r") | target.starts_with("armv7r") {
+                    if target.starts_with("armeb") {
+                        cmd.args.push("-mbig-endian".into());
+                    } else {
+                        cmd.args.push("-mlittle-endian".into());
+                    }
+
+                    // ARM mode
+                    cmd.args.push("-marm".into());
+
+                    // R Profile
+                    cmd.args.push("-march=armv7-r".into());
+
+                    if target.ends_with("eabihf") {
+                        // Calling convention
+                        cmd.args.push("-mfloat-abi=hard".into());
+
+                        // lowest common denominator FPU
+                        // (see Cortex-R4 technical reference manual)
+                        cmd.args.push("-mfpu=vfpv3-d16".into())
+                    } else {
+                        // Calling convention
+                        cmd.args.push("-mfloat-abi=soft".into());
+                    }
+                }
+                if target.starts_with("armv7a") {
+                    cmd.args.push("-march=armv7-a".into());
+
+                    if target.ends_with("eabihf") {
+                        // lowest common denominator FPU
+                        cmd.args.push("-mfpu=vfpv3-d16".into());
+                    }
+                }
+                if target.starts_with("riscv32") || target.starts_with("riscv64") {
+                    // get the 32i/32imac/32imc/64gc/64imac/... part
+                    let mut parts = target.split('-');
+                    if let Some(arch) = parts.next() {
+                        let arch = &arch[5..];
+                        if target.contains("linux") && arch.starts_with("64") {
+                            cmd.args.push(("-march=rv64gc").into());
+                            cmd.args.push("-mabi=lp64d".into());
+                        } else if target.contains("freebsd") && arch.starts_with("64") {
+                            cmd.args.push(("-march=rv64gc").into());
+                            cmd.args.push("-mabi=lp64d".into());
+                        } else if target.contains("openbsd") && arch.starts_with("64") {
+                            cmd.args.push(("-march=rv64gc").into());
+                            cmd.args.push("-mabi=lp64d".into());
+                        } else if target.contains("linux") && arch.starts_with("32") {
+                            cmd.args.push(("-march=rv32gc").into());
+                            cmd.args.push("-mabi=ilp32d".into());
+                        } else if arch.starts_with("64") {
+                            cmd.args.push(("-march=rv".to_owned() + arch).into());
+                            cmd.args.push("-mabi=lp64".into());
+                        } else {
+                            cmd.args.push(("-march=rv".to_owned() + arch).into());
+                            cmd.args.push("-mabi=ilp32".into());
+                        }
+                        cmd.args.push("-mcmodel=medany".into());
+                    }
+                }
+            }
+        }
+
+        if target.contains("apple-ios") {
+            self.ios_flags(cmd)?;
+        }
+
+        if self.static_flag.unwrap_or(false) {
+            cmd.args.push("-static".into());
+        }
+        if self.shared_flag.unwrap_or(false) {
+            cmd.args.push("-shared".into());
+        }
+
+        if self.cpp {
+            match (self.cpp_set_stdlib.as_ref(), cmd.family) {
+                (None, _) => {}
+                (Some(stdlib), ToolFamily::Gnu) | (Some(stdlib), ToolFamily::Clang) => {
+                    cmd.push_cc_arg(format!("-stdlib=lib{}", stdlib).into());
+                }
+                _ => {
+                    println!(
+                        "cargo:warning=cpp_set_stdlib is specified, but the {:?} compiler \
+                         does not support this option, ignored",
+                        cmd.family
+                    );
+                }
+            }
+        }
+
+        Ok(())
+    }
+
+    fn has_flags(&self) -> bool {
+        let flags_env_var_name = if self.cpp { "CXXFLAGS" } else { "CFLAGS" };
+        let flags_env_var_value = self.get_var(flags_env_var_name);
+        if let Ok(_) = flags_env_var_value {
+            true
+        } else {
+            false
+        }
+    }
+
+    fn msvc_macro_assembler(&self) -> Result<(Command, String), Error> {
+        let target = self.get_target()?;
+        let tool = if target.contains("x86_64") {
+            "ml64.exe"
+        } else if target.contains("arm") {
+            "armasm.exe"
+        } else if target.contains("aarch64") {
+            "armasm64.exe"
+        } else {
+            "ml.exe"
+        };
+        let mut cmd = windows_registry::find(&target, tool).unwrap_or_else(|| self.cmd(tool));
+        cmd.arg("-nologo"); // undocumented, yet working with armasm[64]
+        for directory in self.include_directories.iter() {
+            cmd.arg("-I").arg(directory);
+        }
+        if target.contains("aarch64") || target.contains("arm") {
+            println!("cargo:warning=The MSVC ARM assemblers do not support -D flags");
+        } else {
+            for &(ref key, ref value) in self.definitions.iter() {
+                if let Some(ref value) = *value {
+                    cmd.arg(&format!("-D{}={}", key, value));
+                } else {
+                    cmd.arg(&format!("-D{}", key));
+                }
+            }
+        }
+
+        if target.contains("i686") || target.contains("i586") {
+            cmd.arg("-safeseh");
+        }
+        for flag in self.flags.iter() {
+            cmd.arg(flag);
+        }
+
+        Ok((cmd, tool.to_string()))
+    }
+
+    fn assemble(&self, lib_name: &str, dst: &Path, objs: &[Object]) -> Result<(), Error> {
+        // Delete the destination if it exists as we want to
+        // create on the first iteration instead of appending.
+        let _ = fs::remove_file(&dst);
+
+        // Add objects to the archive in limited-length batches. This helps keep
+        // the length of the command line within a reasonable length to avoid
+        // blowing system limits on limiting platforms like Windows.
+        let objs: Vec<_> = objs
+            .iter()
+            .map(|o| o.dst.clone())
+            .chain(self.objects.clone())
+            .collect();
+        for chunk in objs.chunks(100) {
+            self.assemble_progressive(dst, chunk)?;
+        }
+
+        if self.cuda {
+            // Link the device-side code and add it to the target library,
+            // so that non-CUDA linker can link the final binary.
+
+            let out_dir = self.get_out_dir()?;
+            let dlink = out_dir.join(lib_name.to_owned() + "_dlink.o");
+            let mut nvcc = self.get_compiler().to_command();
+            nvcc.arg("--device-link")
+                .arg("-o")
+                .arg(dlink.clone())
+                .arg(dst);
+            run(&mut nvcc, "nvcc")?;
+            self.assemble_progressive(dst, &[dlink])?;
+        }
+
+        let target = self.get_target()?;
+        if target.contains("msvc") {
+            // The Rust compiler will look for libfoo.a and foo.lib, but the
+            // MSVC linker will also be passed foo.lib, so be sure that both
+            // exist for now.
+
+            let lib_dst = dst.with_file_name(format!("{}.lib", lib_name));
+            let _ = fs::remove_file(&lib_dst);
+            match fs::hard_link(&dst, &lib_dst).or_else(|_| {
+                // if hard-link fails, just copy (ignoring the number of bytes written)
+                fs::copy(&dst, &lib_dst).map(|_| ())
+            }) {
+                Ok(_) => (),
+                Err(_) => {
+                    return Err(Error::new(
+                        ErrorKind::IOError,
+                        "Could not copy or create a hard-link to the generated lib file.",
+                    ));
+                }
+            };
+        } else {
+            // Non-msvc targets (those using `ar`) need a separate step to add
+            // the symbol table to archives since our construction command of
+            // `cq` doesn't add it for us.
+            let (mut ar, cmd) = self.get_ar()?;
+            run(ar.arg("s").arg(dst), &cmd)?;
+        }
+
+        Ok(())
+    }
+
+    fn assemble_progressive(&self, dst: &Path, objs: &[PathBuf]) -> Result<(), Error> {
+        let target = self.get_target()?;
+
+        if target.contains("msvc") {
+            let (mut cmd, program) = self.get_ar()?;
+            let mut out = OsString::from("-out:");
+            out.push(dst);
+            cmd.arg(out).arg("-nologo");
+            for flag in self.ar_flags.iter() {
+                cmd.arg(flag);
+            }
+            // If the library file already exists, add the library name
+            // as an argument to let lib.exe know we are appending the objs.
+            if dst.exists() {
+                cmd.arg(dst);
+            }
+            cmd.args(objs);
+            run(&mut cmd, &program)?;
+        } else {
+            let (mut ar, cmd) = self.get_ar()?;
+
+            // Set an environment variable to tell the OSX archiver to ensure
+            // that all dates listed in the archive are zero, improving
+            // determinism of builds. AFAIK there's not really official
+            // documentation of this but there's a lot of references to it if
+            // you search google.
+            //
+            // You can reproduce this locally on a mac with:
+            //
+            //      $ touch foo.c
+            //      $ cc -c foo.c -o foo.o
+            //
+            //      # Notice that these two checksums are different
+            //      $ ar crus libfoo1.a foo.o && sleep 2 && ar crus libfoo2.a foo.o
+            //      $ md5sum libfoo*.a
+            //
+            //      # Notice that these two checksums are the same
+            //      $ export ZERO_AR_DATE=1
+            //      $ ar crus libfoo1.a foo.o && sleep 2 && touch foo.o && ar crus libfoo2.a foo.o
+            //      $ md5sum libfoo*.a
+            //
+            // In any case if this doesn't end up getting read, it shouldn't
+            // cause that many issues!
+            ar.env("ZERO_AR_DATE", "1");
+            for flag in self.ar_flags.iter() {
+                ar.arg(flag);
+            }
+            run(ar.arg("cq").arg(dst).args(objs), &cmd)?;
+        }
+
+        Ok(())
+    }
+
+    fn ios_flags(&self, cmd: &mut Tool) -> Result<(), Error> {
+        enum ArchSpec {
+            Device(&'static str),
+            Simulator(&'static str),
+            Catalyst(&'static str),
+        }
+
+        let target = self.get_target()?;
+        let arch = target.split('-').nth(0).ok_or_else(|| {
+            Error::new(
+                ErrorKind::ArchitectureInvalid,
+                "Unknown architecture for iOS target.",
+            )
+        })?;
+
+        let is_catalyst = match target.split('-').nth(3) {
+            Some(v) => v == "macabi",
+            None => false,
+        };
+
+        let is_sim = match target.split('-').nth(3) {
+            Some(v) => v == "sim",
+            None => false,
+        };
+
+        let arch = if is_catalyst {
+            match arch {
+                "arm64e" => ArchSpec::Catalyst("arm64e"),
+                "arm64" | "aarch64" => ArchSpec::Catalyst("arm64"),
+                "x86_64" => ArchSpec::Catalyst("-m64"),
+                _ => {
+                    return Err(Error::new(
+                        ErrorKind::ArchitectureInvalid,
+                        "Unknown architecture for iOS target.",
+                    ));
+                }
+            }
+        } else if is_sim {
+            match arch {
+                "arm64" | "aarch64" => ArchSpec::Simulator("-arch arm64"),
+                _ => {
+                    return Err(Error::new(
+                        ErrorKind::ArchitectureInvalid,
+                        "Unknown architecture for iOS simulator target.",
+                    ));
+                }
+            }
+        } else {
+            match arch {
+                "arm" | "armv7" | "thumbv7" => ArchSpec::Device("armv7"),
+                "armv7s" | "thumbv7s" => ArchSpec::Device("armv7s"),
+                "arm64e" => ArchSpec::Device("arm64e"),
+                "arm64" | "aarch64" => ArchSpec::Device("arm64"),
+                "i386" | "i686" => ArchSpec::Simulator("-m32"),
+                "x86_64" => ArchSpec::Simulator("-m64"),
+                _ => {
+                    return Err(Error::new(
+                        ErrorKind::ArchitectureInvalid,
+                        "Unknown architecture for iOS target.",
+                    ));
+                }
+            }
+        };
+
+        let min_version =
+            std::env::var("IPHONEOS_DEPLOYMENT_TARGET").unwrap_or_else(|_| "7.0".into());
+
+        let sdk = match arch {
+            ArchSpec::Device(arch) => {
+                cmd.args.push("-arch".into());
+                cmd.args.push(arch.into());
+                cmd.args
+                    .push(format!("-miphoneos-version-min={}", min_version).into());
+                "iphoneos"
+            }
+            ArchSpec::Simulator(arch) => {
+                cmd.args.push(arch.into());
+                cmd.args
+                    .push(format!("-mios-simulator-version-min={}", min_version).into());
+                "iphonesimulator"
+            }
+            ArchSpec::Catalyst(_) => "macosx",
+        };
+
+        self.print(&format!("Detecting iOS SDK path for {}", sdk));
+        let sdk_path = self.apple_sdk_root(sdk)?;
+        cmd.args.push("-isysroot".into());
+        cmd.args.push(sdk_path);
+        cmd.args.push("-fembed-bitcode".into());
+        /*
+         * TODO we probably ultimately want the -fembed-bitcode-marker flag
+         * but can't have it now because of an issue in LLVM:
+         * https://github.com/alexcrichton/cc-rs/issues/301
+         * https://github.com/rust-lang/rust/pull/48896#comment-372192660
+         */
+        /*
+        if self.get_opt_level()? == "0" {
+            cmd.args.push("-fembed-bitcode-marker".into());
+        }
+        */
+
+        Ok(())
+    }
+
+    fn cmd<P: AsRef<OsStr>>(&self, prog: P) -> Command {
+        let mut cmd = Command::new(prog);
+        for &(ref a, ref b) in self.env.iter() {
+            cmd.env(a, b);
+        }
+        cmd
+    }
+
+    fn get_base_compiler(&self) -> Result<Tool, Error> {
+        if let Some(ref c) = self.compiler {
+            return Ok(Tool::new(c.clone()));
+        }
+        let host = self.get_host()?;
+        let target = self.get_target()?;
+        let (env, msvc, gnu, traditional, clang) = if self.cpp {
+            ("CXX", "cl.exe", "g++", "c++", "clang++")
+        } else {
+            ("CC", "cl.exe", "gcc", "cc", "clang")
+        };
+
+        // On historical Solaris systems, "cc" may have been Sun Studio, which
+        // is not flag-compatible with "gcc".  This history casts a long shadow,
+        // and many modern illumos distributions today ship GCC as "gcc" without
+        // also making it available as "cc".
+        let default = if host.contains("solaris") || host.contains("illumos") {
+            gnu
+        } else {
+            traditional
+        };
+
+        let cl_exe = windows_registry::find_tool(&target, "cl.exe");
+
+        let tool_opt: Option<Tool> = self
+            .env_tool(env)
+            .map(|(tool, wrapper, args)| {
+                // find the driver mode, if any
+                const DRIVER_MODE: &str = "--driver-mode=";
+                let driver_mode = args
+                    .iter()
+                    .find(|a| a.starts_with(DRIVER_MODE))
+                    .map(|a| &a[DRIVER_MODE.len()..]);
+                // Chop off leading/trailing whitespace to work around
+                // semi-buggy build scripts which are shared in
+                // makefiles/configure scripts (where spaces are far more
+                // lenient)
+                let mut t = Tool::with_clang_driver(PathBuf::from(tool.trim()), driver_mode);
+                if let Some(cc_wrapper) = wrapper {
+                    t.cc_wrapper_path = Some(PathBuf::from(cc_wrapper));
+                }
+                for arg in args {
+                    t.cc_wrapper_args.push(arg.into());
+                }
+                t
+            })
+            .or_else(|| {
+                if target.contains("emscripten") {
+                    let tool = if self.cpp { "em++" } else { "emcc" };
+                    // Windows uses bat file so we have to be a bit more specific
+                    if cfg!(windows) {
+                        let mut t = Tool::new(PathBuf::from("cmd"));
+                        t.args.push("/c".into());
+                        t.args.push(format!("{}.bat", tool).into());
+                        Some(t)
+                    } else {
+                        Some(Tool::new(PathBuf::from(tool)))
+                    }
+                } else {
+                    None
+                }
+            })
+            .or_else(|| cl_exe.clone());
+
+        let tool = match tool_opt {
+            Some(t) => t,
+            None => {
+                let compiler = if host.contains("windows") && target.contains("windows") {
+                    if target.contains("msvc") {
+                        msvc.to_string()
+                    } else {
+                        format!("{}.exe", gnu)
+                    }
+                } else if target.contains("apple-ios") {
+                    clang.to_string()
+                } else if target.contains("android") {
+                    autodetect_android_compiler(&target, &host, gnu, clang)
+                } else if target.contains("cloudabi") {
+                    format!("{}-{}", target, traditional)
+                } else if target == "wasm32-wasi"
+                    || target == "wasm32-unknown-wasi"
+                    || target == "wasm32-unknown-unknown"
+                {
+                    "clang".to_string()
+                } else if target.contains("vxworks") {
+                    if self.cpp {
+                        "wr-c++".to_string()
+                    } else {
+                        "wr-cc".to_string()
+                    }
+                } else if target.starts_with("armv7a-kmc-solid_") {
+                    format!("arm-kmc-eabi-{}", gnu)
+                } else if target.starts_with("aarch64-kmc-solid_") {
+                    format!("aarch64-kmc-elf-{}", gnu)
+                } else if self.get_host()? != target {
+                    let prefix = self.prefix_for_target(&target);
+                    match prefix {
+                        Some(prefix) => format!("{}-{}", prefix, gnu),
+                        None => default.to_string(),
+                    }
+                } else {
+                    default.to_string()
+                };
+
+                let mut t = Tool::new(PathBuf::from(compiler));
+                if let Some(cc_wrapper) = Self::rustc_wrapper_fallback() {
+                    t.cc_wrapper_path = Some(PathBuf::from(cc_wrapper));
+                }
+                t
+            }
+        };
+
+        let mut tool = if self.cuda {
+            assert!(
+                tool.args.is_empty(),
+                "CUDA compilation currently assumes empty pre-existing args"
+            );
+            let nvcc = match self.get_var("NVCC") {
+                Err(_) => "nvcc".into(),
+                Ok(nvcc) => nvcc,
+            };
+            let mut nvcc_tool = Tool::with_features(PathBuf::from(nvcc), None, self.cuda);
+            nvcc_tool
+                .args
+                .push(format!("-ccbin={}", tool.path.display()).into());
+            nvcc_tool.family = tool.family;
+            nvcc_tool
+        } else {
+            tool
+        };
+
+        // New "standalone" C/C++ cross-compiler executables from recent Android NDK
+        // are just shell scripts that call main clang binary (from Android NDK) with
+        // proper `--target` argument.
+        //
+        // For example, armv7a-linux-androideabi16-clang passes
+        // `--target=armv7a-linux-androideabi16` to clang.
+        //
+        // As the shell script calls the main clang binary, the command line limit length
+        // on Windows is restricted to around 8k characters instead of around 32k characters.
+        // To remove this limit, we call the main clang binary directly and construct the
+        // `--target=` ourselves.
+        if host.contains("windows") && android_clang_compiler_uses_target_arg_internally(&tool.path)
+        {
+            if let Some(path) = tool.path.file_name() {
+                let file_name = path.to_str().unwrap().to_owned();
+                let (target, clang) = file_name.split_at(file_name.rfind("-").unwrap());
+
+                tool.path.set_file_name(clang.trim_start_matches("-"));
+                tool.path.set_extension("exe");
+                tool.args.push(format!("--target={}", target).into());
+
+                // Additionally, shell scripts for target i686-linux-android versions 16 to 24
+                // pass the `mstackrealign` option so we do that here as well.
+                if target.contains("i686-linux-android") {
+                    let (_, version) = target.split_at(target.rfind("d").unwrap() + 1);
+                    if let Ok(version) = version.parse::<u32>() {
+                        if version > 15 && version < 25 {
+                            tool.args.push("-mstackrealign".into());
+                        }
+                    }
+                }
+            };
+        }
+
+        // If we found `cl.exe` in our environment, the tool we're returning is
+        // an MSVC-like tool, *and* no env vars were set then set env vars for
+        // the tool that we're returning.
+        //
+        // Env vars are needed for things like `link.exe` being put into PATH as
+        // well as header include paths sometimes. These paths are automatically
+        // included by default but if the `CC` or `CXX` env vars are set these
+        // won't be used. This'll ensure that when the env vars are used to
+        // configure for invocations like `clang-cl` we still get a "works out
+        // of the box" experience.
+        if let Some(cl_exe) = cl_exe {
+            if tool.family == (ToolFamily::Msvc { clang_cl: true })
+                && tool.env.len() == 0
+                && target.contains("msvc")
+            {
+                for &(ref k, ref v) in cl_exe.env.iter() {
+                    tool.env.push((k.to_owned(), v.to_owned()));
+                }
+            }
+        }
+
+        Ok(tool)
+    }
+
+    fn get_var(&self, var_base: &str) -> Result<String, Error> {
+        let target = self.get_target()?;
+        let host = self.get_host()?;
+        let kind = if host == target { "HOST" } else { "TARGET" };
+        let target_u = target.replace("-", "_");
+        let res = self
+            .getenv(&format!("{}_{}", var_base, target))
+            .or_else(|| self.getenv(&format!("{}_{}", var_base, target_u)))
+            .or_else(|| self.getenv(&format!("{}_{}", kind, var_base)))
+            .or_else(|| self.getenv(var_base));
+
+        match res {
+            Some(res) => Ok(res),
+            None => Err(Error::new(
+                ErrorKind::EnvVarNotFound,
+                &format!("Could not find environment variable {}.", var_base),
+            )),
+        }
+    }
+
+    fn envflags(&self, name: &str) -> Vec<String> {
+        self.get_var(name)
+            .unwrap_or(String::new())
+            .split_ascii_whitespace()
+            .map(|slice| slice.to_string())
+            .collect()
+    }
+
+    /// Returns a fallback `cc_compiler_wrapper` by introspecting `RUSTC_WRAPPER`
+    fn rustc_wrapper_fallback() -> Option<String> {
+        // No explicit CC wrapper was detected, but check if RUSTC_WRAPPER
+        // is defined and is a build accelerator that is compatible with
+        // C/C++ compilers (e.g. sccache)
+        const VALID_WRAPPERS: &[&'static str] = &["sccache", "cachepot"];
+
+        let rustc_wrapper = std::env::var_os("RUSTC_WRAPPER")?;
+        let wrapper_path = Path::new(&rustc_wrapper);
+        let wrapper_stem = wrapper_path.file_stem()?;
+
+        if VALID_WRAPPERS.contains(&wrapper_stem.to_str()?) {
+            Some(rustc_wrapper.to_str()?.to_owned())
+        } else {
+            None
+        }
+    }
+
+    /// Returns compiler path, optional modifier name from whitelist, and arguments vec
+    fn env_tool(&self, name: &str) -> Option<(String, Option<String>, Vec<String>)> {
+        let tool = match self.get_var(name) {
+            Ok(tool) => tool,
+            Err(_) => return None,
+        };
+
+        // If this is an exact path on the filesystem we don't want to do any
+        // interpretation at all, just pass it on through. This'll hopefully get
+        // us to support spaces-in-paths.
+        if Path::new(&tool).exists() {
+            return Some((tool, None, Vec::new()));
+        }
+
+        // Ok now we want to handle a couple of scenarios. We'll assume from
+        // here on out that spaces are splitting separate arguments. Two major
+        // features we want to support are:
+        //
+        //      CC='sccache cc'
+        //
+        // aka using `sccache` or any other wrapper/caching-like-thing for
+        // compilations. We want to know what the actual compiler is still,
+        // though, because our `Tool` API support introspection of it to see
+        // what compiler is in use.
+        //
+        // additionally we want to support
+        //
+        //      CC='cc -flag'
+        //
+        // where the CC env var is used to also pass default flags to the C
+        // compiler.
+        //
+        // It's true that everything here is a bit of a pain, but apparently if
+        // you're not literally make or bash then you get a lot of bug reports.
+        let known_wrappers = ["ccache", "distcc", "sccache", "icecc", "cachepot"];
+
+        let mut parts = tool.split_whitespace();
+        let maybe_wrapper = match parts.next() {
+            Some(s) => s,
+            None => return None,
+        };
+
+        let file_stem = Path::new(maybe_wrapper)
+            .file_stem()
+            .unwrap()
+            .to_str()
+            .unwrap();
+        if known_wrappers.contains(&file_stem) {
+            if let Some(compiler) = parts.next() {
+                return Some((
+                    compiler.to_string(),
+                    Some(maybe_wrapper.to_string()),
+                    parts.map(|s| s.to_string()).collect(),
+                ));
+            }
+        }
+
+        Some((
+            maybe_wrapper.to_string(),
+            Self::rustc_wrapper_fallback(),
+            parts.map(|s| s.to_string()).collect(),
+        ))
+    }
+
+    /// Returns the C++ standard library:
+    /// 1. If [cpp_link_stdlib](cc::Build::cpp_link_stdlib) is set, uses its value.
+    /// 2. Else if the `CXXSTDLIB` environment variable is set, uses its value.
+    /// 3. Else the default is `libc++` for OS X and BSDs, `libc++_shared` for Android,
+    /// `None` for MSVC and `libstdc++` for anything else.
+    fn get_cpp_link_stdlib(&self) -> Result<Option<String>, Error> {
+        match self.cpp_link_stdlib.clone() {
+            Some(s) => Ok(s),
+            None => {
+                if let Ok(stdlib) = self.get_var("CXXSTDLIB") {
+                    if stdlib.is_empty() {
+                        Ok(None)
+                    } else {
+                        Ok(Some(stdlib))
+                    }
+                } else {
+                    let target = self.get_target()?;
+                    if target.contains("msvc") {
+                        Ok(None)
+                    } else if target.contains("apple") {
+                        Ok(Some("c++".to_string()))
+                    } else if target.contains("freebsd") {
+                        Ok(Some("c++".to_string()))
+                    } else if target.contains("openbsd") {
+                        Ok(Some("c++".to_string()))
+                    } else if target.contains("android") {
+                        Ok(Some("c++_shared".to_string()))
+                    } else {
+                        Ok(Some("stdc++".to_string()))
+                    }
+                }
+            }
+        }
+    }
+
+    fn get_ar(&self) -> Result<(Command, String), Error> {
+        if let Some(ref p) = self.archiver {
+            let name = p.file_name().and_then(|s| s.to_str()).unwrap_or("ar");
+            return Ok((self.cmd(p), name.to_string()));
+        }
+        if let Ok(p) = self.get_var("AR") {
+            return Ok((self.cmd(&p), p));
+        }
+        let target = self.get_target()?;
+        let default_ar = "ar".to_string();
+        let program = if target.contains("android") {
+            format!("{}-ar", target.replace("armv7", "arm"))
+        } else if target.contains("emscripten") {
+            // Windows use bat files so we have to be a bit more specific
+            if cfg!(windows) {
+                let mut cmd = self.cmd("cmd");
+                cmd.arg("/c").arg("emar.bat");
+                return Ok((cmd, "emar.bat".to_string()));
+            }
+
+            "emar".to_string()
+        } else if target.contains("msvc") {
+            match windows_registry::find(&target, "lib.exe") {
+                Some(t) => return Ok((t, "lib.exe".to_string())),
+                None => "lib.exe".to_string(),
+            }
+        } else if target.contains("illumos") {
+            // The default 'ar' on illumos uses a non-standard flags,
+            // but the OS comes bundled with a GNU-compatible variant.
+            //
+            // Use the GNU-variant to match other Unix systems.
+            "gar".to_string()
+        } else if self.get_host()? != target {
+            match self.prefix_for_target(&target) {
+                Some(p) => {
+                    let target_ar = format!("{}-ar", p);
+                    if Command::new(&target_ar).output().is_ok() {
+                        target_ar
+                    } else {
+                        default_ar
+                    }
+                }
+                None => default_ar,
+            }
+        } else {
+            default_ar
+        };
+        Ok((self.cmd(&program), program))
+    }
+
+    fn prefix_for_target(&self, target: &str) -> Option<String> {
+        // CROSS_COMPILE is of the form: "arm-linux-gnueabi-"
+        let cc_env = self.getenv("CROSS_COMPILE");
+        let cross_compile = cc_env
+            .as_ref()
+            .map(|s| s.trim_right_matches('-').to_owned());
+        cross_compile.or(match &target[..] {
+            "aarch64-pc-windows-gnu" => Some("aarch64-w64-mingw32"),
+            "aarch64-uwp-windows-gnu" => Some("aarch64-w64-mingw32"),
+            "aarch64-unknown-linux-gnu" => Some("aarch64-linux-gnu"),
+            "aarch64-unknown-linux-musl" => Some("aarch64-linux-musl"),
+            "aarch64-unknown-netbsd" => Some("aarch64--netbsd"),
+            "arm-unknown-linux-gnueabi" => Some("arm-linux-gnueabi"),
+            "armv4t-unknown-linux-gnueabi" => Some("arm-linux-gnueabi"),
+            "armv5te-unknown-linux-gnueabi" => Some("arm-linux-gnueabi"),
+            "armv5te-unknown-linux-musleabi" => Some("arm-linux-gnueabi"),
+            "arm-frc-linux-gnueabi" => Some("arm-frc-linux-gnueabi"),
+            "arm-unknown-linux-gnueabihf" => Some("arm-linux-gnueabihf"),
+            "arm-unknown-linux-musleabi" => Some("arm-linux-musleabi"),
+            "arm-unknown-linux-musleabihf" => Some("arm-linux-musleabihf"),
+            "arm-unknown-netbsd-eabi" => Some("arm--netbsdelf-eabi"),
+            "armv6-unknown-netbsd-eabihf" => Some("armv6--netbsdelf-eabihf"),
+            "armv7-unknown-linux-gnueabi" => Some("arm-linux-gnueabi"),
+            "armv7-unknown-linux-gnueabihf" => Some("arm-linux-gnueabihf"),
+            "armv7-unknown-linux-musleabihf" => Some("arm-linux-musleabihf"),
+            "armv7neon-unknown-linux-gnueabihf" => Some("arm-linux-gnueabihf"),
+            "armv7neon-unknown-linux-musleabihf" => Some("arm-linux-musleabihf"),
+            "thumbv7-unknown-linux-gnueabihf" => Some("arm-linux-gnueabihf"),
+            "thumbv7-unknown-linux-musleabihf" => Some("arm-linux-musleabihf"),
+            "thumbv7neon-unknown-linux-gnueabihf" => Some("arm-linux-gnueabihf"),
+            "thumbv7neon-unknown-linux-musleabihf" => Some("arm-linux-musleabihf"),
+            "armv7-unknown-netbsd-eabihf" => Some("armv7--netbsdelf-eabihf"),
+            "hexagon-unknown-linux-musl" => Some("hexagon-linux-musl"),
+            "i586-unknown-linux-musl" => Some("musl"),
+            "i686-pc-windows-gnu" => Some("i686-w64-mingw32"),
+            "i686-uwp-windows-gnu" => Some("i686-w64-mingw32"),
+            "i686-unknown-linux-gnu" => self.find_working_gnu_prefix(&[
+                "i686-linux-gnu",
+                "x86_64-linux-gnu", // transparently support gcc-multilib
+            ]), // explicit None if not found, so caller knows to fall back
+            "i686-unknown-linux-musl" => Some("musl"),
+            "i686-unknown-netbsd" => Some("i486--netbsdelf"),
+            "mips-unknown-linux-gnu" => Some("mips-linux-gnu"),
+            "mips-unknown-linux-musl" => Some("mips-linux-musl"),
+            "mipsel-unknown-linux-gnu" => Some("mipsel-linux-gnu"),
+            "mipsel-unknown-linux-musl" => Some("mipsel-linux-musl"),
+            "mips64-unknown-linux-gnuabi64" => Some("mips64-linux-gnuabi64"),
+            "mips64el-unknown-linux-gnuabi64" => Some("mips64el-linux-gnuabi64"),
+            "mipsisa32r6-unknown-linux-gnu" => Some("mipsisa32r6-linux-gnu"),
+            "mipsisa32r6el-unknown-linux-gnu" => Some("mipsisa32r6el-linux-gnu"),
+            "mipsisa64r6-unknown-linux-gnuabi64" => Some("mipsisa64r6-linux-gnuabi64"),
+            "mipsisa64r6el-unknown-linux-gnuabi64" => Some("mipsisa64r6el-linux-gnuabi64"),
+            "powerpc-unknown-linux-gnu" => Some("powerpc-linux-gnu"),
+            "powerpc-unknown-linux-gnuspe" => Some("powerpc-linux-gnuspe"),
+            "powerpc-unknown-netbsd" => Some("powerpc--netbsd"),
+            "powerpc64-unknown-linux-gnu" => Some("powerpc-linux-gnu"),
+            "powerpc64le-unknown-linux-gnu" => Some("powerpc64le-linux-gnu"),
+            "riscv32i-unknown-none-elf" => self.find_working_gnu_prefix(&[
+                "riscv32-unknown-elf",
+                "riscv64-unknown-elf",
+                "riscv-none-embed",
+            ]),
+            "riscv32imac-unknown-none-elf" => self.find_working_gnu_prefix(&[
+                "riscv32-unknown-elf",
+                "riscv64-unknown-elf",
+                "riscv-none-embed",
+            ]),
+            "riscv32imc-unknown-none-elf" => self.find_working_gnu_prefix(&[
+                "riscv32-unknown-elf",
+                "riscv64-unknown-elf",
+                "riscv-none-embed",
+            ]),
+            "riscv64gc-unknown-none-elf" => self.find_working_gnu_prefix(&[
+                "riscv64-unknown-elf",
+                "riscv32-unknown-elf",
+                "riscv-none-embed",
+            ]),
+            "riscv64imac-unknown-none-elf" => self.find_working_gnu_prefix(&[
+                "riscv64-unknown-elf",
+                "riscv32-unknown-elf",
+                "riscv-none-embed",
+            ]),
+            "riscv64gc-unknown-linux-gnu" => Some("riscv64-linux-gnu"),
+            "riscv32gc-unknown-linux-gnu" => Some("riscv32-linux-gnu"),
+            "riscv64gc-unknown-linux-musl" => Some("riscv64-linux-musl"),
+            "riscv32gc-unknown-linux-musl" => Some("riscv32-linux-musl"),
+            "s390x-unknown-linux-gnu" => Some("s390x-linux-gnu"),
+            "sparc-unknown-linux-gnu" => Some("sparc-linux-gnu"),
+            "sparc64-unknown-linux-gnu" => Some("sparc64-linux-gnu"),
+            "sparc64-unknown-netbsd" => Some("sparc64--netbsd"),
+            "sparcv9-sun-solaris" => Some("sparcv9-sun-solaris"),
+            "armv7a-none-eabi" => Some("arm-none-eabi"),
+            "armv7a-none-eabihf" => Some("arm-none-eabi"),
+            "armebv7r-none-eabi" => Some("arm-none-eabi"),
+            "armebv7r-none-eabihf" => Some("arm-none-eabi"),
+            "armv7r-none-eabi" => Some("arm-none-eabi"),
+            "armv7r-none-eabihf" => Some("arm-none-eabi"),
+            "thumbv6m-none-eabi" => Some("arm-none-eabi"),
+            "thumbv7em-none-eabi" => Some("arm-none-eabi"),
+            "thumbv7em-none-eabihf" => Some("arm-none-eabi"),
+            "thumbv7m-none-eabi" => Some("arm-none-eabi"),
+            "thumbv8m.base-none-eabi" => Some("arm-none-eabi"),
+            "thumbv8m.main-none-eabi" => Some("arm-none-eabi"),
+            "thumbv8m.main-none-eabihf" => Some("arm-none-eabi"),
+            "x86_64-pc-windows-gnu" => Some("x86_64-w64-mingw32"),
+            "x86_64-uwp-windows-gnu" => Some("x86_64-w64-mingw32"),
+            "x86_64-rumprun-netbsd" => Some("x86_64-rumprun-netbsd"),
+            "x86_64-unknown-linux-gnu" => self.find_working_gnu_prefix(&[
+                "x86_64-linux-gnu", // rustfmt wrap
+            ]), // explicit None if not found, so caller knows to fall back
+            "x86_64-unknown-linux-musl" => Some("musl"),
+            "x86_64-unknown-netbsd" => Some("x86_64--netbsd"),
+            _ => None,
+        }
+        .map(|x| x.to_owned()))
+    }
+
+    /// Some platforms have multiple, compatible, canonical prefixes. Look through
+    /// each possible prefix for a compiler that exists and return it. The prefixes
+    /// should be ordered from most-likely to least-likely.
+    fn find_working_gnu_prefix(&self, prefixes: &[&'static str]) -> Option<&'static str> {
+        let suffix = if self.cpp { "-g++" } else { "-gcc" };
+        let extension = std::env::consts::EXE_SUFFIX;
+
+        // Loop through PATH entries searching for each toolchain. This ensures that we
+        // are more likely to discover the toolchain early on, because chances are good
+        // that the desired toolchain is in one of the higher-priority paths.
+        env::var_os("PATH")
+            .as_ref()
+            .and_then(|path_entries| {
+                env::split_paths(path_entries).find_map(|path_entry| {
+                    for prefix in prefixes {
+                        let target_compiler = format!("{}{}{}", prefix, suffix, extension);
+                        if path_entry.join(&target_compiler).exists() {
+                            return Some(prefix);
+                        }
+                    }
+                    None
+                })
+            })
+            .map(|prefix| *prefix)
+            .or_else(||
+            // If no toolchain was found, provide the first toolchain that was passed in.
+            // This toolchain has been shown not to exist, however it will appear in the
+            // error that is shown to the user which should make it easier to search for
+            // where it should be obtained.
+            prefixes.first().map(|prefix| *prefix))
+    }
+
+    fn get_target(&self) -> Result<String, Error> {
+        match self.target.clone() {
+            Some(t) => Ok(t),
+            None => Ok(self.getenv_unwrap("TARGET")?),
+        }
+    }
+
+    fn get_host(&self) -> Result<String, Error> {
+        match self.host.clone() {
+            Some(h) => Ok(h),
+            None => Ok(self.getenv_unwrap("HOST")?),
+        }
+    }
+
+    fn get_opt_level(&self) -> Result<String, Error> {
+        match self.opt_level.as_ref().cloned() {
+            Some(ol) => Ok(ol),
+            None => Ok(self.getenv_unwrap("OPT_LEVEL")?),
+        }
+    }
+
+    fn get_debug(&self) -> bool {
+        self.debug.unwrap_or_else(|| match self.getenv("DEBUG") {
+            Some(s) => s != "false",
+            None => false,
+        })
+    }
+
+    fn get_force_frame_pointer(&self) -> bool {
+        self.force_frame_pointer.unwrap_or_else(|| self.get_debug())
+    }
+
+    fn get_out_dir(&self) -> Result<PathBuf, Error> {
+        match self.out_dir.clone() {
+            Some(p) => Ok(p),
+            None => Ok(env::var_os("OUT_DIR").map(PathBuf::from).ok_or_else(|| {
+                Error::new(
+                    ErrorKind::EnvVarNotFound,
+                    "Environment variable OUT_DIR not defined.",
+                )
+            })?),
+        }
+    }
+
+    fn getenv(&self, v: &str) -> Option<String> {
+        let mut cache = self.env_cache.lock().unwrap();
+        if let Some(val) = cache.get(v) {
+            return val.clone();
+        }
+        let r = env::var(v).ok();
+        self.print(&format!("{} = {:?}", v, r));
+        cache.insert(v.to_string(), r.clone());
+        r
+    }
+
+    fn getenv_unwrap(&self, v: &str) -> Result<String, Error> {
+        match self.getenv(v) {
+            Some(s) => Ok(s),
+            None => Err(Error::new(
+                ErrorKind::EnvVarNotFound,
+                &format!("Environment variable {} not defined.", v.to_string()),
+            )),
+        }
+    }
+
+    fn print(&self, s: &str) {
+        if self.cargo_metadata {
+            println!("{}", s);
+        }
+    }
+
+    fn fix_env_for_apple_os(&self, cmd: &mut Command) -> Result<(), Error> {
+        let target = self.get_target()?;
+        let host = self.get_host()?;
+        if host.contains("apple-darwin") && target.contains("apple-darwin") {
+            // If, for example, `cargo` runs during the build of an XCode project, then `SDKROOT` environment variable
+            // would represent the current target, and this is the problem for us, if we want to compile something
+            // for the host, when host != target.
+            // We can not just remove `SDKROOT`, because, again, for example, XCode add to PATH
+            // /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
+            // and `cc` from this path can not find system include files, like `pthread.h`, if `SDKROOT`
+            // is not set
+            if let Ok(sdkroot) = env::var("SDKROOT") {
+                if !sdkroot.contains("MacOSX") {
+                    let macos_sdk = self.apple_sdk_root("macosx")?;
+                    cmd.env("SDKROOT", macos_sdk);
+                }
+            }
+            // Additionally, `IPHONEOS_DEPLOYMENT_TARGET` must not be set when using the Xcode linker at
+            // "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld",
+            // although this is apparently ignored when using the linker at "/usr/bin/ld".
+            cmd.env_remove("IPHONEOS_DEPLOYMENT_TARGET");
+        }
+        Ok(())
+    }
+
+    fn apple_sdk_root(&self, sdk: &str) -> Result<OsString, Error> {
+        let mut cache = self
+            .apple_sdk_root_cache
+            .lock()
+            .expect("apple_sdk_root_cache lock failed");
+        if let Some(ret) = cache.get(sdk) {
+            return Ok(ret.clone());
+        }
+
+        let sdk_path = run_output(
+            self.cmd("xcrun")
+                .arg("--show-sdk-path")
+                .arg("--sdk")
+                .arg(sdk),
+            "xcrun",
+        )?;
+
+        let sdk_path = match String::from_utf8(sdk_path) {
+            Ok(p) => p,
+            Err(_) => {
+                return Err(Error::new(
+                    ErrorKind::IOError,
+                    "Unable to determine iOS SDK path.",
+                ));
+            }
+        };
+        let ret: OsString = sdk_path.trim().into();
+        cache.insert(sdk.into(), ret.clone());
+        Ok(ret)
+    }
+}
+
+impl Default for Build {
+    fn default() -> Build {
+        Build::new()
+    }
+}
+
+impl Tool {
+    fn new(path: PathBuf) -> Self {
+        Tool::with_features(path, None, false)
+    }
+
+    fn with_clang_driver(path: PathBuf, clang_driver: Option<&str>) -> Self {
+        Self::with_features(path, clang_driver, false)
+    }
+
+    #[cfg(windows)]
+    /// Explicitly set the `ToolFamily`, skipping name-based detection.
+    fn with_family(path: PathBuf, family: ToolFamily) -> Self {
+        Self {
+            path: path,
+            cc_wrapper_path: None,
+            cc_wrapper_args: Vec::new(),
+            args: Vec::new(),
+            env: Vec::new(),
+            family: family,
+            cuda: false,
+            removed_args: Vec::new(),
+        }
+    }
+
+    fn with_features(path: PathBuf, clang_driver: Option<&str>, cuda: bool) -> Self {
+        // Try to detect family of the tool from its name, falling back to Gnu.
+        let family = if let Some(fname) = path.file_name().and_then(|p| p.to_str()) {
+            if fname.contains("clang-cl") {
+                ToolFamily::Msvc { clang_cl: true }
+            } else if fname.ends_with("cl") || fname == "cl.exe" {
+                ToolFamily::Msvc { clang_cl: false }
+            } else if fname.contains("clang") {
+                match clang_driver {
+                    Some("cl") => ToolFamily::Msvc { clang_cl: true },
+                    _ => ToolFamily::Clang,
+                }
+            } else {
+                ToolFamily::Gnu
+            }
+        } else {
+            ToolFamily::Gnu
+        };
+
+        Tool {
+            path: path,
+            cc_wrapper_path: None,
+            cc_wrapper_args: Vec::new(),
+            args: Vec::new(),
+            env: Vec::new(),
+            family: family,
+            cuda: cuda,
+            removed_args: Vec::new(),
+        }
+    }
+
+    /// Add an argument to be stripped from the final command arguments.
+    fn remove_arg(&mut self, flag: OsString) {
+        self.removed_args.push(flag);
+    }
+
+    /// Add a flag, and optionally prepend the NVCC wrapper flag "-Xcompiler".
+    ///
+    /// Currently this is only used for compiling CUDA sources, since NVCC only
+    /// accepts a limited set of GNU-like flags, and the rest must be prefixed
+    /// with a "-Xcompiler" flag to get passed to the underlying C++ compiler.
+    fn push_cc_arg(&mut self, flag: OsString) {
+        if self.cuda {
+            self.args.push("-Xcompiler".into());
+        }
+        self.args.push(flag);
+    }
+
+    fn is_duplicate_opt_arg(&self, flag: &OsString) -> bool {
+        let flag = flag.to_str().unwrap();
+        let mut chars = flag.chars();
+
+        // Only duplicate check compiler flags
+        if self.is_like_msvc() {
+            if chars.next() != Some('/') {
+                return false;
+            }
+        } else if self.is_like_gnu() || self.is_like_clang() {
+            if chars.next() != Some('-') {
+                return false;
+            }
+        }
+
+        // Check for existing optimization flags (-O, /O)
+        if chars.next() == Some('O') {
+            return self
+                .args()
+                .iter()
+                .any(|ref a| a.to_str().unwrap_or("").chars().nth(1) == Some('O'));
+        }
+
+        // TODO Check for existing -m..., -m...=..., /arch:... flags
+        return false;
+    }
+
+    /// Don't push optimization arg if it conflicts with existing args
+    fn push_opt_unless_duplicate(&mut self, flag: OsString) {
+        if self.is_duplicate_opt_arg(&flag) {
+            println!("Info: Ignoring duplicate arg {:?}", &flag);
+        } else {
+            self.push_cc_arg(flag);
+        }
+    }
+
+    /// Converts this compiler into a `Command` that's ready to be run.
+    ///
+    /// This is useful for when the compiler needs to be executed and the
+    /// command returned will already have the initial arguments and environment
+    /// variables configured.
+    pub fn to_command(&self) -> Command {
+        let mut cmd = match self.cc_wrapper_path {
+            Some(ref cc_wrapper_path) => {
+                let mut cmd = Command::new(&cc_wrapper_path);
+                cmd.arg(&self.path);
+                cmd
+            }
+            None => Command::new(&self.path),
+        };
+        cmd.args(&self.cc_wrapper_args);
+
+        let value = self
+            .args
+            .iter()
+            .filter(|a| !self.removed_args.contains(a))
+            .collect::<Vec<_>>();
+        cmd.args(&value);
+
+        for &(ref k, ref v) in self.env.iter() {
+            cmd.env(k, v);
+        }
+        cmd
+    }
+
+    /// Returns the path for this compiler.
+    ///
+    /// Note that this may not be a path to a file on the filesystem, e.g. "cc",
+    /// but rather something which will be resolved when a process is spawned.
+    pub fn path(&self) -> &Path {
+        &self.path
+    }
+
+    /// Returns the default set of arguments to the compiler needed to produce
+    /// executables for the target this compiler generates.
+    pub fn args(&self) -> &[OsString] {
+        &self.args
+    }
+
+    /// Returns the set of environment variables needed for this compiler to
+    /// operate.
+    ///
+    /// This is typically only used for MSVC compilers currently.
+    pub fn env(&self) -> &[(OsString, OsString)] {
+        &self.env
+    }
+
+    /// Returns the compiler command in format of CC environment variable.
+    /// Or empty string if CC env was not present
+    ///
+    /// This is typically used by configure script
+    pub fn cc_env(&self) -> OsString {
+        match self.cc_wrapper_path {
+            Some(ref cc_wrapper_path) => {
+                let mut cc_env = cc_wrapper_path.as_os_str().to_owned();
+                cc_env.push(" ");
+                cc_env.push(self.path.to_path_buf().into_os_string());
+                for arg in self.cc_wrapper_args.iter() {
+                    cc_env.push(" ");
+                    cc_env.push(arg);
+                }
+                cc_env
+            }
+            None => OsString::from(""),
+        }
+    }
+
+    /// Returns the compiler flags in format of CFLAGS environment variable.
+    /// Important here - this will not be CFLAGS from env, its internal gcc's flags to use as CFLAGS
+    /// This is typically used by configure script
+    pub fn cflags_env(&self) -> OsString {
+        let mut flags = OsString::new();
+        for (i, arg) in self.args.iter().enumerate() {
+            if i > 0 {
+                flags.push(" ");
+            }
+            flags.push(arg);
+        }
+        flags
+    }
+
+    /// Whether the tool is GNU Compiler Collection-like.
+    pub fn is_like_gnu(&self) -> bool {
+        self.family == ToolFamily::Gnu
+    }
+
+    /// Whether the tool is Clang-like.
+    pub fn is_like_clang(&self) -> bool {
+        self.family == ToolFamily::Clang
+    }
+
+    /// Whether the tool is MSVC-like.
+    pub fn is_like_msvc(&self) -> bool {
+        match self.family {
+            ToolFamily::Msvc { .. } => true,
+            _ => false,
+        }
+    }
+}
+
+fn run(cmd: &mut Command, program: &str) -> Result<(), Error> {
+    let (mut child, print) = spawn(cmd, program)?;
+    let status = match child.wait() {
+        Ok(s) => s,
+        Err(_) => {
+            return Err(Error::new(
+                ErrorKind::ToolExecError,
+                &format!(
+                    "Failed to wait on spawned child process, command {:?} with args {:?}.",
+                    cmd, program
+                ),
+            ));
+        }
+    };
+    print.join().unwrap();
+    println!("{}", status);
+
+    if status.success() {
+        Ok(())
+    } else {
+        Err(Error::new(
+            ErrorKind::ToolExecError,
+            &format!(
+                "Command {:?} with args {:?} did not execute successfully (status code {}).",
+                cmd, program, status
+            ),
+        ))
+    }
+}
+
+fn run_output(cmd: &mut Command, program: &str) -> Result<Vec<u8>, Error> {
+    cmd.stdout(Stdio::piped());
+    let (mut child, print) = spawn(cmd, program)?;
+    let mut stdout = vec![];
+    child
+        .stdout
+        .take()
+        .unwrap()
+        .read_to_end(&mut stdout)
+        .unwrap();
+    let status = match child.wait() {
+        Ok(s) => s,
+        Err(_) => {
+            return Err(Error::new(
+                ErrorKind::ToolExecError,
+                &format!(
+                    "Failed to wait on spawned child process, command {:?} with args {:?}.",
+                    cmd, program
+                ),
+            ));
+        }
+    };
+    print.join().unwrap();
+    println!("{}", status);
+
+    if status.success() {
+        Ok(stdout)
+    } else {
+        Err(Error::new(
+            ErrorKind::ToolExecError,
+            &format!(
+                "Command {:?} with args {:?} did not execute successfully (status code {}).",
+                cmd, program, status
+            ),
+        ))
+    }
+}
+
+fn spawn(cmd: &mut Command, program: &str) -> Result<(Child, JoinHandle<()>), Error> {
+    println!("running: {:?}", cmd);
+
+    // Capture the standard error coming from these programs, and write it out
+    // with cargo:warning= prefixes. Note that this is a bit wonky to avoid
+    // requiring the output to be UTF-8, we instead just ship bytes from one
+    // location to another.
+    match cmd.stderr(Stdio::piped()).spawn() {
+        Ok(mut child) => {
+            let stderr = BufReader::new(child.stderr.take().unwrap());
+            let print = thread::spawn(move || {
+                for line in stderr.split(b'\n').filter_map(|l| l.ok()) {
+                    print!("cargo:warning=");
+                    std::io::stdout().write_all(&line).unwrap();
+                    println!("");
+                }
+            });
+            Ok((child, print))
+        }
+        Err(ref e) if e.kind() == io::ErrorKind::NotFound => {
+            let extra = if cfg!(windows) {
+                " (see https://github.com/alexcrichton/cc-rs#compile-time-requirements \
+                 for help)"
+            } else {
+                ""
+            };
+            Err(Error::new(
+                ErrorKind::ToolNotFound,
+                &format!("Failed to find tool. Is `{}` installed?{}", program, extra),
+            ))
+        }
+        Err(ref e) => Err(Error::new(
+            ErrorKind::ToolExecError,
+            &format!(
+                "Command {:?} with args {:?} failed to start: {:?}",
+                cmd, program, e
+            ),
+        )),
+    }
+}
+
+fn fail(s: &str) -> ! {
+    eprintln!("\n\nerror occurred: {}\n\n", s);
+    std::process::exit(1);
+}
+
+fn command_add_output_file(
+    cmd: &mut Command,
+    dst: &Path,
+    cuda: bool,
+    msvc: bool,
+    clang: bool,
+    is_asm: bool,
+    is_arm: bool,
+) {
+    if msvc && !clang && !cuda && !(is_asm && is_arm) {
+        let mut s = OsString::from("-Fo");
+        s.push(&dst);
+        cmd.arg(s);
+    } else {
+        cmd.arg("-o").arg(&dst);
+    }
+}
+
+// Use by default minimum available API level
+// See note about naming here
+// https://android.googlesource.com/platform/ndk/+/refs/heads/ndk-release-r21/docs/BuildSystemMaintainers.md#Clang
+static NEW_STANDALONE_ANDROID_COMPILERS: [&str; 4] = [
+    "aarch64-linux-android21-clang",
+    "armv7a-linux-androideabi16-clang",
+    "i686-linux-android16-clang",
+    "x86_64-linux-android21-clang",
+];
+
+// New "standalone" C/C++ cross-compiler executables from recent Android NDK
+// are just shell scripts that call main clang binary (from Android NDK) with
+// proper `--target` argument.
+//
+// For example, armv7a-linux-androideabi16-clang passes
+// `--target=armv7a-linux-androideabi16` to clang.
+// So to construct proper command line check if
+// `--target` argument would be passed or not to clang
+fn android_clang_compiler_uses_target_arg_internally(clang_path: &Path) -> bool {
+    if let Some(filename) = clang_path.file_name() {
+        if let Some(filename_str) = filename.to_str() {
+            filename_str.contains("android")
+        } else {
+            false
+        }
+    } else {
+        false
+    }
+}
+
+#[test]
+fn test_android_clang_compiler_uses_target_arg_internally() {
+    for version in 16..21 {
+        assert!(android_clang_compiler_uses_target_arg_internally(
+            &PathBuf::from(format!("armv7a-linux-androideabi{}-clang", version))
+        ));
+        assert!(android_clang_compiler_uses_target_arg_internally(
+            &PathBuf::from(format!("armv7a-linux-androideabi{}-clang++", version))
+        ));
+    }
+    assert!(!android_clang_compiler_uses_target_arg_internally(
+        &PathBuf::from("clang")
+    ));
+    assert!(!android_clang_compiler_uses_target_arg_internally(
+        &PathBuf::from("clang++")
+    ));
+}
+
+fn autodetect_android_compiler(target: &str, host: &str, gnu: &str, clang: &str) -> String {
+    let new_clang_key = match target {
+        "aarch64-linux-android" => Some("aarch64"),
+        "armv7-linux-androideabi" => Some("armv7a"),
+        "i686-linux-android" => Some("i686"),
+        "x86_64-linux-android" => Some("x86_64"),
+        _ => None,
+    };
+
+    let new_clang = new_clang_key
+        .map(|key| {
+            NEW_STANDALONE_ANDROID_COMPILERS
+                .iter()
+                .find(|x| x.starts_with(key))
+        })
+        .unwrap_or(None);
+
+    if let Some(new_clang) = new_clang {
+        if Command::new(new_clang).output().is_ok() {
+            return (*new_clang).into();
+        }
+    }
+
+    let target = target
+        .replace("armv7neon", "arm")
+        .replace("armv7", "arm")
+        .replace("thumbv7neon", "arm")
+        .replace("thumbv7", "arm");
+    let gnu_compiler = format!("{}-{}", target, gnu);
+    let clang_compiler = format!("{}-{}", target, clang);
+
+    // On Windows, the Android clang compiler is provided as a `.cmd` file instead
+    // of a `.exe` file. `std::process::Command` won't run `.cmd` files unless the
+    // `.cmd` is explicitly appended to the command name, so we do that here.
+    let clang_compiler_cmd = format!("{}-{}.cmd", target, clang);
+
+    // Check if gnu compiler is present
+    // if not, use clang
+    if Command::new(&gnu_compiler).output().is_ok() {
+        gnu_compiler
+    } else if host.contains("windows") && Command::new(&clang_compiler_cmd).output().is_ok() {
+        clang_compiler_cmd
+    } else {
+        clang_compiler
+    }
+}
+
+// Rust and clang/cc don't agree on how to name the target.
+fn map_darwin_target_from_rust_to_compiler_architecture(target: &str) -> Option<&'static str> {
+    if target.contains("x86_64") {
+        Some("x86_64")
+    } else if target.contains("arm64e") {
+        Some("arm64e")
+    } else if target.contains("aarch64") {
+        Some("arm64")
+    } else if target.contains("i686") {
+        Some("i386")
+    } else if target.contains("powerpc") {
+        Some("ppc")
+    } else if target.contains("powerpc64") {
+        Some("ppc64")
+    } else {
+        None
+    }
+}
+
+fn which(tool: &Path) -> Option<PathBuf> {
+    fn check_exe(exe: &mut PathBuf) -> bool {
+        let exe_ext = std::env::consts::EXE_EXTENSION;
+        exe.exists() || (!exe_ext.is_empty() && exe.set_extension(exe_ext) && exe.exists())
+    }
+
+    // If |tool| is not just one "word," assume it's an actual path...
+    if tool.components().count() > 1 {
+        let mut exe = PathBuf::from(tool);
+        return if check_exe(&mut exe) { Some(exe) } else { None };
+    }
+
+    // Loop through PATH entries searching for the |tool|.
+    let path_entries = env::var_os("PATH")?;
+    env::split_paths(&path_entries).find_map(|path_entry| {
+        let mut exe = path_entry.join(tool);
+        return if check_exe(&mut exe) { Some(exe) } else { None };
+    })
+}